Begin by bringing a large pot of salted water to a boil. Carefully add the jumbo pasta shells and cook until al dente, about 9-11 minutes. Drain and rinse with cold water.

In a large skillet over medium heat, cook the ground beef until browned, about 6-8 minutes. Season with salt, pepper, garlic powder, and Italian seasoning. Drain excess fat.

In a mixing bowl, combine ricotta, half the mozzarella, and parmesan with the cooked beef. Mix thoroughly.

Preheat oven to 350°F (175°C). Spread marinara sauce in a baking dish. Stuff each shell with the cheese and beef mixture and arrange in the dish.

Cover filled shells with remaining marinara sauce and sprinkle with rest of the mozzarella. Bake for 30-40 minutes until bubbly and golden.