Preheat your oven to 350°F (175°C). In a large pot, boil salted water and gently add the jumbo pasta shells. Cook for about 8-10 minutes, then drain and rinse with cold water. Lay on a baking sheet to cool.

In a large skillet, heat olive oil over medium heat. Add chopped onion and sauté until soft, about 3-4 minutes. Stir in minced garlic and sauté for an additional minute, then add ground beef. Cook until browned, about 5-7 minutes. Drain excess fat, mix in Italian seasoning and spaghetti sauce, and set aside to cool slightly.

In a mixing bowl, combine ricotta cheese, ½ cup shredded mozzarella, grated Parmesan, and one beaten egg. Stir until smooth, then fold in the beef filling until fully incorporated.

Grease a baking dish with olive oil. Pour a layer of spaghetti sauce across the bottom. Carefully fill each pasta shell with the beef and cheese mixture, placing seam side up in the dish.

Sprinkle remaining mozzarella and Parmesan cheese over the stuffed shells. Cover loosely with foil and bake for 25-30 minutes. Remove the foil and bake for an additional 5-10 minutes until golden and bubbly.

Let cool for a few minutes before serving. Garnish with fresh herbs if desired.