Preheat your oven to 350°F (175°C). Boil a pot of salted water, then cook the jumbo pasta shells until al dente, about 8-10 minutes. Drain and cool them under cold water.

In a skillet, heat olive oil over medium heat. Sauté chopped onions until translucent, add minced garlic and ground beef. Season with salt, pepper, and Italian seasoning, mixing in spaghetti sauce. Let the filling cool.

In a large bowl, combine ricotta, shredded mozzarella, grated Parmesan, and a beaten egg. Gently fold in the cooled beef mixture.

Lightly grease a baking dish with olive oil. Spread a thin layer of spaghetti sauce on the bottom, fill each pasta shell, and arrange them in the dish.

Sprinkle extra mozzarella and Parmesan over the stuffed shells. Cover with foil and bake for 25-30 minutes. Remove foil for the last 5-10 minutes.

Allow shells to cool slightly before serving. Garnish with fresh herbs if desired and serve with garlic bread or salad.