Preheat oven to 350 degrees F.

Cook frozen chopped spinach per package instructions. Remove from heat; drain WELL. Let spinach cool.

In a medium sized mixing bowl, combine the ricotta cheese, grated mozzarella, Parmesan cheese, parsley, salt, pepper, garlic powder and ground oregano. Stir well until fully combined.

Add spinach to the cheese mixture. Stir well, to combine.

Cook manicotti shells according to package instructions (add to boiling water-7 minutes cook time is typical). When done, remove from heat, drain gently, and let dry.

Fill each shell using a spoon until full of filling.

Spread some of the spaghetti sauce over the bottom of 13x9 baking pan (enough to fully cover); put the filled pasta in a single layer on top of sauce.

Spoon the rest of the spaghetti sauce over the top of the manicotti. Sprinkle with additional grated Parmesan cheese (or mozzarella), if desired. Cover pan with aluminum foil.

Bake at 350 degrees for 40 minutes; remove foil, then cook an additional 15 minutes. Manicotti should be hot and cheese bubbly when done. Remove pan from oven. Let sit for a minute or two, then gently remove manicotti to individual serving plates using a spatula.

Serve with a green salad and a slice of crusty french bread, and enjoy!