Preheat oven to 375 degrees F.

Cook shells according to package directions until Al Dente ( approximately 10 minutes). Immerse shells in cold water to cool and place on paper towel to dry.

Meanwhile, heat the butter in a large pan over medium heat and saute onion, garlic, peppers and mushroom until tender. Place in a bowl and allow to cool to room temperature. When cooled, add ricotta, beaten egg, 1/2 cup of the parmesan, basil, half of the parsley, oregano, breadcrumbs, salt and pepper. Mix well. Mixture should be firm but still moist.

Cover the bottom of a large glass baking dish with enough tomato sauce to cover. Gently stuff the shells with the cheese mixture and place in dish on tomato sauce. Spoon the rest of the tomato sauce over the shells and sprinkle with the rest of the parmesan cheese and parsley. Bake covered for 20 to 30 minutes and cook uncovered for 5 to 10. Let stand 10 minutes and serve with additional parmesan and garnish with sprigs of parsley and basil if desired.