1. Heat a large deep skillet or Dutch oven over medium-high heat. Add olive oil if needed, then add the ground beef and cook for 5 to 6 minutes, breaking it apart, until browned. Drain excess grease.

2. Add the diced onion and cook for 3 to 4 minutes until softened. Stir in the garlic and cook for 30 seconds.

3. Sprinkle in the taco seasoning, add the tomato paste, and stir for 1 minute to deepen the flavor.

4. Pour in the diced tomatoes with green chiles, tomato sauce, and beef broth. Stir well, scraping the bottom of the pot.

5. Add the pasta shells and bring the mixture to a gentle boil. Reduce heat to medium-low, cover, and simmer for 12 to 15 minutes, stirring often, until the pasta is tender.

6. Lower the heat and stir in the cream cheese until melted and smooth.

7. Add cheddar cheese and Monterey Jack cheese a handful at a time, stirring until creamy.

8. Season with salt and black pepper to taste, then let the pasta rest for 3 to 5 minutes.

9. Garnish with fresh cilantro and serve warm with sour cream, avocado, jalapeños, lime wedges, or crushed tortilla chips if desired.