Remove stems from mushrooms and set aside. Rub mushrooms with olive oil. Mince mushroom stems and set aside.
In skillet, cook sausage. Add onion, green pepper and garlic, and continue to sauté for another few minutes. Remove from heat and set aside.
Mix bread crumbs and Parmesan in a bowl, reserving 3 tablespoons for the topping.
In a bowl, add remaining ingredients, bread crumb mixture, mushroom stems, sausage mixture, and gently stir. Divide the mixture evenly over the 2 mushrooms, then top with the remaining bread crumb mixture.
Bake at 400°F for 15 minutes.