Preheat your oven to 350°F (175°C). Cook the jumbo shells for about 7 minutes until they are soft. Drain them.

In a skillet over medium heat, cook the diced onion and ground beef until the beef is browned and crumbled. Add the taco seasoning and crushed tomatoes. Stir until heated through and bubbly. Drain any excess liquid using a mesh colander.

Spread 1 cup of salsa on the bottom of a 9x13-inch baking dish. Fill each pasta shell with around 2 tablespoons of the beef mixture and place them open side up in the dish, close together.

Sprinkle the shredded cheese over the shells.

Cover the dish with aluminum foil, making sure it doesn't touch the cheese. Bake for 15-20 minutes until the cheese is melted and bubbly.

Add your favorite taco toppings like shredded lettuce, diced tomatoes, sour cream, cilantro, and green onions. Serve the Taco Stuffed Shells warm.