Thinly slice onion and place in the bottom of a crockpot. Drain and rinse beans.
Rub chicken thighs with salt and pepper then lay them on top of the onions.
Add the beans, corn, and 1 cup salsa to the chicken, then sprinkle with cumin and paprika.
Cover and cook on low for 4-5 hours until chicken is cooked through and shreds easily with a fork.
Before serving, heat a dry skillet over high heat. Add tortillas–cooking one at at time–and heat about 20 seconds per side until just beginning to brown. Wrap in foil and place in a 200° F oven to keep warm.
When ready to eat, fill each tortilla with chicken and black bean mixture. Top with diced tomato, shredded lettuce, sour cream, cheese and salsa, if desired. Serve with apple slices.