Preheat oven to 400F degrees.
Heat a skillet over medium high heat, when hot, add the olive oil. Add the mushrooms and the onions, and saute until slightly soft, about 2 minutes.
On the flatbread, spread the basil pesto, avoiding the outer one inch edge. Top the flat bread with the mozzarella cheese. Add the mushroom and onion mixture; and top with the parmesan cheese.
Bake for 7 to 10 minutes until the cheese has melted and the flatbread is toasted. Sprinkle with the fresh basil.