Preheat oven to 425 degrees. Spray a baking sheet with vegetable spray and set aside.
In a medium bowl, combine mustard, olive oil, garlic, rosemary, salt and pepper. Whisk to combine. Add potatoes and toss until potatoes are well coated.
Arrange potatoes on the baking sheet, preferably flesh side down (this promotes a nice browning and crisping).
Roast for 15 minutes. Sprinkle the potatoes with lemon zest and flip them with a spatula to coat.
Return the potatoes to the oven and continue cooking for an additional 15 minutes until crispy on the outside and tender inside. Sprinkle with parsley. Serve.
Video
Notes
These potatoes are excellent served hot but also can be served at room temperature with a chop of fresh parsley.