Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells according to package instructions until al dente.
In a skillet, brown the ground beef over medium heat; drain excess fat.
Add garlic powder, Italian seasoning, salt, and pepper to the beef.
In a bowl, mix ricotta cheese, egg, and half of the mozzarella and Parmesan cheeses.
Combine the beef mixture with the cheese mixture until well blended.
Stuff each cooked shell with the beef and cheese mixture.
Spread a layer of marinara sauce in a baking dish.
Arrange the stuffed shells in the dish and top with remaining marinara sauce.
Sprinkle the remaining mozzarella and Parmesan cheeses on top.
Bake for 25-30 minutes until cheese is bubbly and golden.