Cook spinach in a small amount of water to which beef bouillon cubes have been added.
Drain and set aside.
Saute onion in margarine.
Stir in bread crumbs, eggs, parmesan cheese, garlic, peppers, and drained spinach.
Add salt to taste.
Arrange sliced tomatoes in a large flat casserole.
Top each slice with mounds of the spinach mixture.
Bake at 350° about 15 to 20 minutes.