In a large slow cooker, add the enchilada sauce, undrained tomatoes, kidney beans, black beans, corn, and uncooked chicken breasts. Add in the chicken stock and all of the seasonings. Mix well.
Cover and cook on high for 3-5 hours, low for 5-8 hours or when the chicken will easily shred. Remove the chicken from the crockpot and shred in another bowl using two forks. Meanwhile, add the Greek yogurt to the slow cooker and stir until well combined. Add the shredded chicken back into the crockpot. Stir until the chicken is combined.