Slice the onions and broccoli and toss with the olive oil. Roast on 475ºF for about 10 minutes.
Meanwhile, mix together the ricotta cheese, minced garlic, and red pepper flakes. Place flatbread on baking sheet or pizza stone. Spread ricotta mixture over flatbread.
When veggies are ready, arrange on flatbread and top with roasted bell pepper slices. Sprinkle with salt and pepper. (And optional Parmesan cheese.) Bake on sheet, pizza stone, or directly on wire rack for 8 minutes on 425ºF.
Notes
Consider swapping out the broccoli for asparagus. And, to save time, you can use a fresh bell pepper instead of roasted bell peppers. In this case, slice the pepper thinly and cook it with the vegetables in step 1.