Over medium heat, use 1 tsp of butter to sautee spinach. Add in garlic powder while spinach is sauteing. After spinach wilts, heat tomatoes slices over medium heat for about 30 seconds on each side, just enough to warm tomatoes. While tomatoes are heating, add basil (if using fresh basil leaves, add leaves to sandwich.
Over medium low heat, fry or scramble egg (cook to preferred consistency but fried or scrambled is highly recommended). Once egg is cooked, layer sandwich starting with bread, one slice of mozzarella, tomatoes, spinach, second slice of cheese, cooked egg, and top slice of bread.