Preheat your oven to 375°F (190°C).

In a large pot, bring salted water to a rolling boil and cook the large pasta shells for about 8 minutes until al dente. Drain and toss with olive oil.

In a skillet, heat olive oil and brown the ground beef for 7-10 minutes. Drain excess fat and set aside.

In a bowl, combine browned beef, ricotta, half of the mozzarella, Parmesan, egg, Italian seasoning, salt, and pepper. Mix well.

Stuff each cooked shell with the filling and arrange them seam-side up in a baking dish.

Spread a thin layer of marinara at the bottom, place the stuffed shells, cover with remaining marinara, and top with remaining mozzarella.

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