Cook ground beef and onions: Brown ground beef in a large skillet over medium, stirring constantly, 5 to 8 minutes or until meat crumbles and is no longer pink; drain. Add onions, and cook until tender and translucent. Add one package of taco seasoning, and stir until meat is covered.
Add ingredients to slow cooker: Spoon ground beef mixture in the bottom of the slow-cooker crock. Add remaining ingredients, and stir to combine.
Cook soup: Cook on HIGH for 4 hours or LOW 6 hours, stirring occasionally.
Serve: Ladle into bowls, top with preferred garnishes, and serve.
