Preheat the oven to 450 degrees. I used mushrooms, grape tomatoes, broccoli, and red peppers. Chop or slice into uniform pieces. Vegetables that take longer to cook like onions should be smaller.
Spray a cookie sheet liberally with cooking spray. Add vegetables and top with chopped garlic and fresh herbs of choice. I used thyme.
Spray vegetables with cooking spray and sprinkle with salt and pepper. Roast for 20 - 25 minutes until vegetables are soft, but not mushy.
Mix 1/2 cup mayonnaise with 1/2 a lemon juiced and 1/2 cup chopped parsley.
Spread sauce, feta cheese and vegetables over flatbread and roll up. Slice in half.