Prep Work: Cut red bell peppers, onion and zucchini; store together. Shred cheese.
Turn on oven broiler to high. Scoop brown gills from bottom side of mushrooms with the edge of a spoon.
Toss garlic, bell pepper, zucchini, onion and mushroom caps together on rimmed baking sheet with enough olive oil to lightly coat all sides; then sprinkle with salt and pepper.
Broil approx. 6" from heat until onions are tender and golden stirring 1-2 times, anywhere from 5-20 minutes (depending on oven). Edges of vegetables should be slightly blackened. Chop mushrooms caps into 1/2" by 1" slices.
Place flat bread on another baking sheet, cover with shredded cheese, and top with roasted vegetables. Place pizzas in oven for a few minutes until cheese melts and then remove.
Slice on a cutting board and serve with green salad. Fresh parmesan cheese, basil and red pepper flakes for optional, additional toppings.
(Inspired by Cooking Light "Grilled Vegetable and Fontina Pizza" Aug. 2012)