Place the ground beef, black beans, pinto beans, diced tomatoes with green chilies, salsa, and taco seasoning directly into the slow cooker.
Stir the ingredients gently to distribute the seasoning evenly through the mixture.
Cover and cook on low for 6 to 7 hours until the beef is fully cooked and the mixture has thickened slightly.
Stir the cooked mixture to break up the beef into smaller pieces.
Spoon the beef and bean mixture over bowls of cooked rice.
Add shredded cheddar cheese and a dollop of sour cream to each bowl before serving.