Spread each bread shell with a scant 3 tablespoons of the Alfredo sauce. Arrange 4 or 5 spinach leaves over sauce; sprinkle with mushrooms. Arrange tomato slices and artichoke hearts over mushrooms. Sprinkle with oregano, then mozzarella cheese.
Place on an extra-large baking sheet. Bake in a 350 degree F oven for about 20 minutes or until cheese is bubbly around edges. Makes 6 servings.