Preheat your oven to 375°F (190°C).
In a large pot, bring salted water to boil. Cook the pasta shells according to package instructions until al dente. Drain and set aside to cool.
In a large skillet over medium heat, cook the ground beef until browned. Drain excess fat if necessary. Stir in marinara sauce, garlic powder, Italian seasoning, salt, and pepper. Let simmer for about 5 minutes.
In a mixing bowl, combine ricotta cheese, ½ cup of mozzarella cheese, grated Parmesan cheese, egg, salt, and pepper. Mix well until smooth.
Carefully fill each pasta shell with the beef mixture, followed by a spoonful of the ricotta mixture. Place stuffed shells in a greased 9x13-inch baking dish.
Pour any remaining marinara sauce over the stuffed shells. Sprinkle the remaining mozzarella cheese on top. Cover with aluminum foil.
Bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 5–10 minutes, or until the cheese is melted and bubbly.
Allow it to cool for a few minutes. Garnish with fresh chopped parsley before serving.