Place the onion. beans corn, tomato sauce,beer and diced tomatoes in a slow cooker. Add taco seasoning and stir to blend. Lay chicken breast on top of the mixture pressing down slightly until just covereed by the other ingredients. Set slow cooker for low heat cover and cook for 5 hours.
remove chicken breast and allow to cool long enough to be handled. Stir in shredded chicken back into soup and continue cooking for 2 hours. Serve topped with shredded cheese a dollop of sour cream and crushed tortilla chips, if desired.