Cook the ground beef and onion in a 6 quart Dutch oven or soup pot over medium high heat until beef is browned and no longer pink, crumbling beef with a wooden spoon while it is cooking (about 5 to 6 minutes). Drain off fat.
Add garlic and cook (while stirring) until garlic is fragrant, about 30 seconds.
Add beef broth, water, tomato paste, diced tomatoes and green chilies, corn, kidney beans, black beans and taco seasoning. Stir to combine.
Bring to just a boil, then reduce heat as necessary to maintain a simmer (medium to medium low).
Simmer for 10 minutes (uncovered), stirring occasionally.
Serve with toppings, if desired.
Notes
To prepare in your slow cooker: brown ground beef with onion in a large skillet over medium high heat and drain off fat. Add garlic and cook until fragrant, while stirring. Transfer mixture into the insert of a 6 quart slow cooker. Add 2 cups beef broth, 1 ½ cups water, tomato paste, diced tomatoes and green chilies, corn, kidney beans, black beans and taco seasoning. Stir to combine. Cover and cook on low heat for 6 hours or high heat for 3 hours.
Dark red or light red kidney beans can be used.
Store in an airtight container in the fridge for up to 3 days, or freeze in freezer bags for up to 6 months.