Easy Mexican Crockpot Chicken

vegetable or canola oil

boneless skinless chicken breasts

Salt and pepper

(16z) cans black beans, undrained

(10z) cans Mexican diced tomatoes

low-sodium taco seasoning {or make your own}

lettuce leaves for serving {alternately, serve over yellow rice}

avocado, diced {optional}

shredded cheddar cheese {optional}

low fat sour cream {optional}

diced scallions or chopped cilantro {optional}