Meanwhile, in a large skillet saute the green pepper, onions and garlic in butter intil tender. Gradually stir in flour until blended. Stir in the shrimp, celery salt and pepper; cook, uncovered, over medium heat for 5 to 6 minutes or until heated through.
In a microwave-safe bowl, combine the process cheese, tomatoes and mushrooms. Microwave, uncovered, on high for 3 to 4 minutes or until cheese is melted, stirring occasionally. Add to shrimp mixture. Drain vermicelli; stir into skillet.
Pour into a greased 13-in. X 9-in. X 2-in. baking dish. Sprinkle with Parmesan cheese. Bake, uncovered, at 350 degrees for 25 to 30 minutes or until heated through.