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, draining excess fat.
Add garlic powder, Italian seasoning, salt, and pepper to the beef.
In a bowl, mix ricotta cheese, mozzarella, and egg until well combined.
Fold the cooked beef into the cheese mixture.
Fill each cooked shell with the beef and cheese mixture.
Spread a layer of marinara sauce in a baking dish.
Place the stuffed shells on top of the sauce.
Top with remaining marinara sauce and sprinkle with Parmesan cheese.
Cover with foil and bake for 20 minutes, then uncover and bake for an additional 10 minutes.