In a medium non-stick skillet, heat oil over medium heat. Or if you have a saute function on your slow cooker, place the oil directly in the slow cooker.
Add the onion, red pepper and garlic, stirring until soft, about 3 minutes. Add to the slow cooker (if you didn't cook it directly in the slow cooker).
Next, add the broth, fire-roasted tomatoes, tomato sauce, black beans, corn, cumin, and oregano, and chipotles in adobe sauce. Stir the mixture until combined.
Add the chicken breasts to the slow cooker, making sure that they're fully covered in the liquid.
Cover and cook on low for 6 to 8 hours or on high for 3 to 4 hours.
Remove the chicken breast and shred it with two forks. Return to the slow cooker. Season with salt and pepper, to taste.
Serve immediately or keep slow cooker on the warm setting until ready to serve. Top with desired toppings.