Heat a large skillet or pot over medium heat and cook ground beef until browned, then drain excess grease.
Add onion and garlic and sauté 2–3 minutes until softened.
Stir in taco seasoning, beef broth, tomato sauce, diced tomatoes, and uncooked pasta.
Bring to a gentle boil, then reduce heat and simmer 12–15 minutes until pasta is tender.
Stir occasionally to prevent sticking and adjust seasoning if needed.
Remove from heat and stir in cheddar and Monterey Jack until melted and creamy.
Let sit 2–3 minutes to thicken slightly before serving.
Garnish with cilantro or sour cream if desired and serve hot.