Preheat your oven to 350°F (175°C).
In a large skillet, cook the ground beef over medium heat until it is browned and crumbled. Drain excess grease.
Add the chopped onion to the skillet and sauté until it is soft.
Cook the pasta according to package instructions and drain.
In a large mixing bowl, combine the cooked beef and onions, cooked pasta, and tomato sauce.
Transfer the mixture into a 9x13 inch baking dish and top with shredded cheddar cheese.
Bake in the preheated oven for 30 minutes, or until the cheese is melted and bubbly.
Remove from oven and let cool for a few minutes before serving.