Preheat oven to 350℉.
Bring a large pot of water to a boil and cook manicotti pasta according to package directions, about 7 minutes. Drain and set aside to cool.
In a large bowl combine, ricotta cheese, half the mozzarella cheese, half the parmesan cheese, 2 eggs, Italian seasoning, salt, pepper, red pepper flakes, and chopped parsley.
Place the filling in a plastic bag and snip off one corner of the bag.
Spread about 1 cup of the marinara sauce in the bottom of an oven safe casserole dish.
Pipe filling into the cooked manicotti shells and place them in a single layer in the casserole dish.
Top with remaining marinara sauce to cover the pasta shells.
Sprinkle with remaining parmesan and mozzarella cheeses.
Cover dish with foil and bake in the oven for 45 minutes.
Remove foil and continue to bake for an additional 15 minutes or until heated through and the cheese is melted, bubbly and hot.
Remove from oven and allow to rest for 5-10 minutes before serving.
To serve, garnish with additional freshly chopped parsley if desired.