Place the onion, beans, corn, tomato paste, beer and tomatoes in the slow cooker. Add taco seasoning and stir to blend. Place chicken on top, pressing them down until covered by ingredients. Set slow cooker on low heat, cover, and cook 5 hours.
Remove chicken breasts from the soup and shred the chicken once its cool enough to handle. Stir shredded chicken back into the soup, and continue cooking for 1-2 hours. Serve topped with shredded cheese, a few dollops of sour cream, and tortilla chips.
And that's it, pretty simple. I cook it on low and then shred the chicken and throw it back in for a half-hour or so and it turns out fine. Pretty delicious and super easy! Makes a full slow cooker so be careful while stirring. You can also toast some tortilla shells to finish it off!