In a large Dutch oven or pot, cook the ground beef and diced onion over medium-high heat, stirring occasionally until the beef is browned and the onion is softened.
Add the chili powder, cumin, smoked paprika, oregano, salt, and black pepper to the pot. Stir to combine and cook for an additional 1 to 2 minutes.
To the taco meat, stir in the uncooked pasta shells, chicken broth, tomato sauce, and Rotel. Bring the mixture to a boil, then reduce the heat to medium-low. Cover the pot and simmer for about 15 minutes, or until the pasta is al dente. Stir occasionally to prevent the pasta from sticking to the bottom of the pot.
Remove the pot from the heat and stir in the shredded cheddar cheese and colby jack cheese a little bit at a time until melted and well combined. Garnish with fresh cilantro (optional) and serve warm.
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Notes
Storage: Leftover pasta should be stored in the refrigerator in an airtight container for up to 3-4 days. Reheat it in the microwave or on the stove until heated through. To freeze, all the pasta to cool completely, then store it in a freezer-safe container for up to 3 months. Thaw it in the refrigerator before reheating.