Preheat your oven to 375°F (190°C).
In a large pot, boil salted water and cook the jumbo pasta shells according to package instructions until al dente. Drain and set aside.
In a medium skillet, heat the olive oil over medium heat. Add the chopped onion and cook until translucent, about 3-4 minutes. Add the minced garlic and cook for another minute.
Add the ground beef to the skillet and season with salt, pepper, and Italian herbs. Cook until the beef is browned and cooked through, breaking it apart with a spoon as it cooks. Drain any excess fat.
In a mixing bowl, combine the cooked beef mixture, ricotta cheese, half of the mozzarella cheese, and the grated Parmesan cheese. Mix well.
Spread 1 cup of marinara sauce in the bottom of a baking dish.
Stuff each cooked pasta shell with the ricotta-beef filling and place them in the baking dish on top of the marinara sauce.
Pour the remaining marinara sauce over the stuffed shells and sprinkle the rest of the mozzarella cheese on top.
Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Let the dish cool for a few minutes before serving. Garnish with fresh basil if desired.