Preheat the oven to 350 degrees F (180 degrees C).
In a pan, add Olive Oil (2 tablespoon), and soften the Onion (1) and Garlic (2 clove). Then, add Frozen Spinach (10 ounce) stir and season with Salt and Pepper (to taste). Cook for about 1 minutes and stir constantly. Transfer to a bowl and set aside.
Mix Ricotta Cheese (2 cup), Cream Cheese (6 ounce), Parmesan Cheese (1/2 cup) with the spinach. Add some Mozzarella Cheese (2 cup) until they are combined. Season with Salt and Pepper (to taste).
Cook the Manicotti Noodles (1 package) for 7 minutes in boiling water and drain.
Take a piping bag and fill in the mixture. Pour the filling in the manicotti. Continue with the rest.
Pour Marinara Sauce (23 ounce) in a baking pan and put the noodles on top and top with the rest of marinara sauce. Cover with foil.
Bake for 25 minutes and sprinkle the remaining mozzarella and bake for another 5 minutes. Serve and enjoy!