In a large mixing bowl, combine the ground beef, chopped onion, minced garlic, and taco seasoning. Mix until well combined.
Transfer the meat mixture into the crockpot, spreading it out evenly.
Add the black beans, diced tomatoes (with juices), tomato sauce, and beef broth to the crockpot. Stir everything together to combine.
Cover and cook on low for 4 hours.
After 4 hours, break the uncooked spaghetti into thirds and stir it into the crockpot. Ensure the pasta is submerged in the sauce.
Cover and cook for an additional 30 minutes on low, or until the spaghetti is cooked to your preference.
Once cooked, stir in the shredded cheddar cheese until melted and well incorporated. Season with salt and pepper to taste.
Serve hot with optional toppings like sour cream, cilantro, or jalapeños.