In a small bowl, combine the mayonnaise, buttermilk, garlic powder, onion powder, Worcestershire sauce, vinegar, cayenne, Dijon, sugar, fish sauce, lemon zest, lemon juice, parsley, chives, tarragon and oregano. Whisk together until smooth and creamy.
Taste for seasonings and add salt and pepper as needed.
Transfer the dressing to a glass container with a lid (I use a canning jar) and refrigerate for several hours so the flavors can marry and the dressing thickens. Serve over salad or with crudite.
Dressing will keep up to one week in the refrigerator.