Add the juice of the limes and the orange to a mixing bowl. Mince garlic and add to juices with chili powder, cumin, oregano, pepper, salt and chopped cilantro. Whisk together.
Slice chicken and place into crockpot. Slice peppers and onion, place on top of chicken in crock pot. Pour in the citrus juice and seasonings.
Cook on low for 3-4 hours.
Place chicken and veggies in tortillas topped with grated cheese and avocado slices.