In a large skillet over medium heat, brown the ground beef (or turkey) along with the diced onion until the meat is cooked through. Drain any excess fat.
Stir in the taco seasoning and mix well to coat the meat evenly.
In the crockpot, combine the cooked meat and onion mixture with black beans, corn, diced tomatoes with green chilies, tomato sauce, and beef broth. Mix to combine thoroughly.
Break the uncooked spaghetti in half and add it to the crockpot, pushing it down into the liquid so it is submerged.
Cover the crockpot and cook on low for 6 hours, or until the spaghetti is cooked and tender.
Just before serving, stir in half of the shredded cheese until melted and combined.
Serve the Taco Spaghetti in bowls, topping with the remaining cheese and any optional toppings you prefer.