In a large soup pot over medium heat, brown ground beef and saute onions until meat is no longer pink and onions are tender. Strain away any excess fat.
Add black beans, sweet corn, both cans of diced tomatoes, taco sauce, diced green chilies, taco seasoning, and chili powder and bring to a boil.
Turn down heat to medium low and let simmer for 25-30 minutes.
Serve with sour cream, cheese, and sliced green onions.
Notes
To make this Taco Chili in the slow cooker, brown the beef and onions in a skillet then transfer to the slow cooker. Add all the other ingredients and then cook on high for 3-4 hours or on low for 6-8 hours.