Brown chopped bacon in a skillet. Add onion, green pepper, and garlic and brown. Stir in flour; add tomatoes and cook until thickened, stirring constantly. Add macaroni, ham and shrimp. Pour into a greased 1 1/2 qt casserole dish. Combine breadcrumbs, cheese and margarine; sprinkle over casserole. Bake at 350 for about 30 minutes.