Preheat your oven to 375°F (190°C).

Cook the pasta: Bring a large pot of salted water to a boil, add the jumbo shells, and cook according to package instructions until al dente. Drain and set aside.

Sauté the onions: In a large skillet, heat a drizzle of olive oil over medium heat. Add the chopped onion, cooking until it's soft and translucent.

Brown the beef: Push the onions to the side and add the ground beef. Break it apart with a spatula, cooking until it’s browned and fully cooked. Drain excess fat if necessary.

Combine: Stir in the cup of salsa and half a cup of each cheese into the beef mixture until well combined.

Stuff the shells: Take each cooked shell and fill it generously with the beef and cheese mixture. Lay the stuffed shells in a greased baking dish, top with the remaining cheese.

Bake: Cover with foil and bake for 20 minutes. Remove foil and bake an additional 10 minutes or until the cheese is melted and bubbly.

Serve: Allow the dish to cool for a few minutes, then serve hot, garnished with fresh herbs or a dollop of sour cream if desired.