Place chicken, & diced onion in crock pot.
Pour in broth, tomatoes, oil, and seasonings.
Cook on low for about 5 hours.
Remove chicken from slow cooker.
Stir precooked rice/quinoa, corn, and black beans, into the hot liquid remaining in crockpot
Let cook an additional 10 minutes on high.
In the meantime, quickly chop, or shred chicken.
Add chicken back in, cook for 10 minutes on high, or just until chicken is hot.
Serve with fresh diced tomatoes, plain Greek yogurt, green onion, diced avocado or guacamole, top with cheese if desired.