Place chopped onions, beans, corn, tomato sauce, tomatoes, and beer into the slow cooker. Mix well.Add taco seasoning and stir to mix together.Place chicken breasts into the mixture, pressing down until covered by mixture.Cook on LOW for 7 hours.Remove chicken from pot and shred with 2 forks.Stir back into crockpot.Serve soup with optional toppings or as is :) DELISH!