1Combine ricotta cheese, mozzarella cheese, frozen chopped spinach, egg, garlic powder, onion powder, oregano, black pepper, and salt in a large mixing bowl.
2Mix the ingredients until well combined.
3Stuff the manicotti shells with the spinach and cheese mixture.
4Pour a layer of tomato sauce in the bottom of a baking dish.
5Place the stuffed manicotti shells on top of the sauce.