Preheat oven to 400F degrees.
Place chicken breasts in a baking dish. Add salt, pepper, taco seasoning, diced onion, drained tomatoes, chipotle peppers, and rinsed and drained black beans.
Bake for 30 minutes, or until chicken is done. Chicken is done when a meat thermometer reads 165F degrees in the thickest part of the chicken.
Remove from the oven and use a fork to shred the chicken.
Fill the taco shells or tortilla shells, add cheese if desired. Brush the outsides of the shells with olive oil to help them brown.
Put back in the oven and bake for about 5 minutes at 375F degrees, until heated through.
Remove from the oven and garnish with chopped cilantro, sour cream, and guacamole if desired.