Heat oil in a medium size skillet over medium heat. Add the diced onion, salt, and cumin, cook until softened and translucent. Add in the garlic and cook an additional 30 seconds until fragrant.
Transfer the cooked onions to the slow cooker and add in the corn, black beans, enchilada sauce, and sour cream. Stir this all together and then add the chicken, coating in the sauce.
Cover and cook on low for 6-7 hours until the chicken is tender. Shred the chicken.
Stir in the tortilla strips and then top with the grated cheese. Cook on low for an additional 30 minutes.
Top with extra sour cream, fresh cilantro and sliced avocado.
Serve this over rice or with tortilla chips as desired.