Preheat oven to 375°F.

Cook manicotti shells in a large pot of boiling salted water until al dente, about 7 minutes. Drain and set aside to cool.

Heat olive oil in a skillet over medium heat. Add ground beef, salt, pepper, garlic powder, and oregano. Cook until beef is browned and fully cooked. Drain excess grease and let cool.

In a bowl, combine ricotta cheese, 1 cup of mozzarella cheese, Parmesan cheese, egg, and the cooled ground beef. Mix well.

Spread 1 cup of marinara sauce on the bottom of a 9x13 inch baking dish.

Fill each manicotti shell with the beef and cheese mixture and place in the baking dish.

Pour the remaining marinara sauce over the stuffed manicotti.

Sprinkle the remaining mozzarella cheese on top.

Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 10 minutes or until cheese is bubbly and golden.

Garnish with grated Parmesan cheese before serving.