Place all ingredients into a large slow cooker (6 quart or larger I used my 6 quart manual crock pot slow cooker) except the cornstarch and 5 tbs of water and cook on high for 8 hours or low for 12+ hours.
An hour before done or serving mix the cornstarch with 5 tbs of cool water and stir into slow cooker to thicken the beans if desired.
Serve over white rice or along side your favorite Mexican recipes.