Place chicken in a slow cooker, pour salsa over top, and sprinkle with taco seasoning.
Cover and cook on low for 4-5 hours or until chicken is cooked through and can be easily shredded with a fork.
Remove cooked chicken from slow cooker, shred, and then return to the pot (or simply shred right there in the crock).
Drain and rinse beans; add to the chicken, along with the corn. Season with salt and pepper to taste and mix well.
Replace the cover and continue cooking on low for about 15 minutes until all ingredients are heated through.
Meanwhile, dice avocados and tomatoes.
When ready to serve, place lettuce onto plates and top with the chicken mixture, cheese, avocado, tomato, and sour cream as desired.