In a large mixing bowl, combine the ground beef, diced onion, bell pepper, and minced garlic. Use your hands or a spoon to mix well.
Transfer the beef mixture into the Crockpot.
Sprinkle the taco seasoning over the beef mixture and stir to combine.
Add the black beans, diced tomatoes, tomato sauce, and chicken broth to the Crockpot. Stir until everything is evenly distributed.
Cover and cook on low heat for 4 hours.
About 30 minutes before serving, break the spaghetti in half and add it to the Crockpot. Stir gently to mix it in with the other ingredients and cover.
Continue to cook for the remaining 30 minutes, until the spaghetti is tender.
Before serving, taste and adjust seasoning with salt and pepper, if needed.