Step 1: Cook the Pasta
Bring a large pot of salted water to a boil.
Cook the jumbo pasta shells until al dente, according to package instructions.
Drain the shells and set them aside to cool.
Step 2: Prepare the Filling
In a skillet, sauté the onion and garlic over medium heat until translucent.
Add the ground beef to the skillet and cook until browned.
Season with Italian seasoning, salt, and pepper.
Allow the beef mixture to cool slightly, then combine it with ricotta, Parmesan, and half of the mozzarella cheese in a mixing bowl.
Step 3: Stuff the Shells
Using a spoon, fill each pasta shell with the beef and cheese mixture.
Step 4: Assemble and Bake
Preheat your oven to 375°F (190°C).
Spread a layer of marinara sauce on the bottom of a baking dish.
Arrange the stuffed shells in the dish, then pour the remaining marinara sauce over the top.
Sprinkle the remaining mozzarella cheese evenly over the shells.
Cover the dish with aluminum foil and bake for 25 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Step 5: Garnish and Serve
Garnish with fresh parsley or basil (optional) and serve hot.