Heat the oil in a large pot over medium heat. Add the onion and pepper, season with salt and pepper and cook for 3-5 minutes or until just softened.
Add the black beans, canned tomatoes, corn, tomato sauce, chicken and taco seasoning. Stir to combine. Add the chicken broth and bring to a simmer. Cook for 15 minutes. Taste and add additional salt and pepper if needed.
Serve the soup immediately, garnished with cilantro, sour cream, and avocado if desired.
Notes
use rotisserie chicken if you want to cut down on time
you may use cooked chicken thighs instead of chicken breast
any other beans of your choice will work instead of black beans
add different toppings of your choice like tortilla chips or shredded cheese