Preheat your oven to 375°F (190°C).
Bring a large pot of salted water to a boil and cook jumbo pasta shells according to package directions until al dente. Drain and set aside to cool slightly.
Heat olive oil in a skillet over medium heat. Add chopped onion and sauté until soft.
Add ground beef and cook until browned, breaking it apart with a spoon. Drain excess grease if needed.
Stir in garlic, Italian seasoning, salt, pepper, and paprika. Cook for another minute, then remove from heat.
In a large bowl, combine cooked beef mixture, ricotta cheese, 1 cup mozzarella, Parmesan, and egg. Mix until well combined.
Spread 1 cup of marinara sauce evenly across the bottom of a baking dish.
Stuff each cooked shell with the beef and cheese filling and arrange them in the dish.
Pour remaining marinara sauce over the shells and sprinkle with the remaining mozzarella cheese.
Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 10–15 minutes until bubbly and lightly golden.
Garnish with fresh herbs and serve warm.