Grilled Portobello Mushroom Sandwich with Basil Aioli

If you like mushrooms, you’ll love this grilled portobello mushroom sandwich. Grilled marinated portobello mushrooms are the foundation of this vegetarian meal, but it doesn’t stop there. With sweet roasted bell peppers, melty gouda cheese and a tasty basil aioli, this portobello sandwich is a winner.

Before we get to the portobello mushroom sandwich, let’s start with the sauce. This basil aioli is the condiment that will tie all of the ingredients together. It’s bright and herbaceous with enough creamy indulgence to to put a smile on your face.

Ingredients For Basil Aioli

• Mayonnaise
• Fresh Basil
• Garlic
• Lemon

Making Basil Aioli For Portobello Sandwich

Get out your blender for this special sauce.

1. In a blender, add the fresh basil and pulse several times to start to break down and chop the herbs.
2. Top the chopped basil with garlic and 3/4 of a cup of mayonnaise and process until the basil and garlic have been thoroughly combined in the mayonnaise. 
3. Add the lemon juice and blend again to combine. The sauce may look a bit curdled, that’s normal. Transfer the aioli to a bowl and add the remaining mayonnaise.
4. Whisk briskly together to smooth out the curdled appearance. 
5. Cover and refrigerate. (You can use the basil aioli immediately, but it will thicken a bit in the refrigerator, so I like to make it an hour or so before serving the portobello mushroom sandwich.

Mushrooms are like sponges, therefore if you submerge them in a marinade, they will absorb a lot of it. To moderate that action, instead of complete soaking the fungi in sauce, brush on the seasoning, so that the marinated portobello gets the flavor without being overpowered by it. I usually brush on the marinade as Scott is preheating the grill, so the marinade has time to soak in to the plump portobellos. I also brush the red onion slices with the marinade as well.

Ingredients For Marinated Portobello

• Garlic 
• Olive Oil
• Worcestershire Sauce
• Balsamic Vinegar
• Kosher Salt
• Freshly Ground Black Pepper

Whisk together all of the ingredients for the marinade and brush over the tops and undersides of the mushrooms as well as the sliced red onions. You want to coat them well  — and you’ll notice that the mushrooms will soak up the moisture quickly.

 For Grilled Portobello Mushroom Sandwich

• Portobello Mushrooms
• Sweet Roasted Bell Peppers (I used red, orange and yellow)
• Red Onions
• Sliced Tomato
• Smoked Gouda
• Whole Wheat Sandwich Rolls

1. Grill the portobello mushrooms on a moderately hot grill for 8-10 minutes, until the mushrooms are tender.
2. Note:  when the mushroom caps are upside down on the grill, liquid will collect in them. Tip the mushrooms over to drain the collected juices, otherwise it will make your sandwiches mushy.
3. If you want melty cheese, after draining the mushroom caps, but while they’re still on the grill, fill them with a few tablespoons of cheese and heat through for about one minute, then transfer the mushrooms to the serving board.
4. Grill the red onions at the same time as the mushrooms. Grilling the onion makes them more tender and adds a smoky char which we like.

I like to serve these portobello sandwiches very casually, presenting the mushroom caps and grilled onions on a carving board along with the condiments and sides. Everyone helps themselves and builds their sandwich according to their tastes and preferences.

During the Spring and Summer months, these grilled, marinated portobello sandwiches are a regular in our dinner rotation. They’re great for meatless Mondays and even my carnivorous husband looks forward to dinner when they’re on the menu. 

To make it vegan, swap vegannaise for the mayonnaise in the aioli and substitute your favorite vegan cheese for the cheddar, monterey jack and gouda.

To make it gluten free: use gluten free rolls or skip the bun altogether and make it a knife and fork meal.

Craving More Veggie Burgers and Sandwiches?

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Southwestern Sweet Potato Quinoa Burger via Dana at Killing Thyme.

Chickpea and Brown Rice Burger via Carmy at Carmy Run Eat Travel.

Carrot Tahini Quinoa Veggie Burger with Tzatziki and Purple Slaw from Tricia at Rhubarbarians.

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Grilled Portobello Burgers

Course: Main Course

Cuisine: American

Keyword: burgers, mushrooms, vegetarian

Dietary Restrictions: Vegetarian

Prep Time: 35 minutes

Cook Time: 10 minutes

Total Time: 45 minutes

Servings: 8

Calories: 542kcal

A yummy vegetarian option for lunch or dinner

Print Recipe

Ingredients

FOR PORTOBELLO SANDWICH

• 3 red bell peppers
• 8 portabella mushroom caps stemmed
• 1 red onion sliced crosswise into 1/2" slices
• 1 1/2 cups shredded or crumbled cheese I used a combination of cheddar, monterey jack and smoked gouda
• basil aioli recipe given
• 8 whole wheat sandwich buns

FOR MARINATED PORTOBELLO

• 3 cloves garlic minced divided in half
• 1/4 cup olive oil
• 1 tablespoon worsterschire sauce
• 1 tablespoon balsamic vinegar
• 1/2 teaspoon kosher salt
• 1/2 teaspoon black pepper freshly ground

FOR BASIL AIOLI

• 1 cup mayonnaise
• 1 cup fresh basil leaves
• remainder of garlic
• squeeze lemon about 1 tablespoon

Instructions

• Heat oven to 375 degrees. Place bell peppers on a baking sheet and roast for 30 minutes until flesh is softened and skin is blackened. Remove peppers from oven and place in a small glass bowl. Cover bowl tightly with cellophane. Let peppers cool until they are comfortable to handle. Peel the skins from the peppers. Pull peppers apart into large chunks and discard seeds and stems. Set aside.
• While peppers cook, use a spoon to scrape the gills from the underside of the mushroom caps. Set aside.

FOR MARINATED PORTOBELLO:

• In a small bowl combine olive oil, worstershire, balsamic, garlic, salt and pepper. Whisk to combine. Set aside.

FOR BASIL AIOLI

•  In a blender or mini-prep food processor add basil leaves, garlic and 3/4 cup of mayonnaise. Pulse until basil is incorporated into the sauce. Add a lemon and pulse again (note: I have a Vitamix blender which can turn concrete into a frothy drink - which is why the color of my aioli is green. With a regular blender/food processor, it probably won't achieve the same color, but the flavor will be there. Promise.) Scrape aioli into a small bowl -- it may look curdled. Add the remainder of the mayonnaise and whisk briskly. The aioli should smooth right out.

FOR PORTOBELLO MUSHROOM SANDWICH

• Heat a grill to a medium high heat - about 375-400 degrees. While grill heats brush mushroom caps and onion slices liberally with marinade.
• Grill mushroom caps and onion until flesh is softened and exterior begins to take on some grill marks. About 8-10 minutes.
• Toast six buns on the grill for just a few minutes, until lightly browned.
• Build burgers. Spread basil aioli on the top and bottom buns. Place mushrooms on the buns, dress with a sprinkle of cheese, a few onion rings and roasted red pepper and tomato.

Nutrition

Calories: 542kcal | Carbohydrates: 29g | Protein: 16g | Fat: 41g | Saturated Fat: 11g | Cholesterol: 54mg | Sodium: 844mg | Potassium: 555mg | Fiber: 4g | Sugar: 9g | Vitamin A: 1785IU | Vitamin C: 58.9mg | Calcium: 321mg | Iron: 2.5mg

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