Cook the pasta according to the package directions until just al dente. Drain.
While the pasta cooks, add the ground beef and diced onion to a large skillet over medium heat. Cook until the beef is browned and the onion is tender. Drain any excess grease.
Add the garlic and taco seasoning. Cook for about 1 minute, then stir in the salsa and tomato sauce. Simmer for 2–3 minutes.
Remove the skillet from the heat and stir in the sour cream and 1/2 cup of the Mexican cheese.
Add the cooked pasta to the skillet and stir until everything is well combined.
Sprinkle the remaining ½ cup Mexican cheese over the top.
Cover the skillet with a lid and let it sit over low heat for 2–4 minutes, or until the cheese is melted.
Remove the lid and top with green onions and cilantro.