Preheat a large frypan over medium heat. Add the oil, chopped onions, capsicum, celery, and garlic. Sauté for 3-5 minutes to soften.
Pour the sautéed veggies and the drained kidney beans in a large slow cooker. Place the chicken over the top, then sprinkle the chili powder, cumin, and salt in the slow cooker.
Pour the jarred roasted red capsicums and their juices in a blender. Puree until very smooth. Pour the pureed red capsicum and chicken stock in the slow cooker. Cover and turn on low for 6-8 hours, or high for 3-4 hours.
When the chicken is cooked through. Remove it with tongs, and shred the chicken with a fork. Stir the shredded chicken back into the crockpot. Serve warm!