In a large bowl, combine ricotta, spinach, onion and egg. Season with parsley, pepper and garlic powder. Mix in 1 cup mozzarella and 1/4 cup Parmesan. In a separate bowl, stir together spaghetti sauce and water.
Spread 1 cup sauce in the bottom of a 9x13 inch baking dish. Stuff uncooked manicotti shells with ricotta mixture, and arrange in a single layer in the dish. Cover with remaining sauce. Sprinkle with remaining mozzarella and Parmesan.
Bake in preheated oven for 45 to 55 minutes, or until noodles are soft.
