Brown the beef:
In a skillet over medium heat, cook the ground beef and chopped onion until the meat is browned and no longer pink. Drain excess grease.
Combine ingredients in crockpot:
Transfer the cooked beef mixture to your slow cooker. Add black beans, kidney beans, corn, diced tomatoes, tomato sauce, beef broth, taco seasoning, chili powder, and cumin. Stir to combine.
Slow cook:
Cover and cook on LOW for 6–8 hours or HIGH for 3–4 hours until the soup is hot and flavorful.
Adjust seasoning:
Taste and adjust salt or pepper as needed before serving.
Serve and garnish:
Ladle into bowls and top with cheese, sour cream, avocado, cilantro, and tortilla chips for that perfect taco-inspired finish.