Preheat large skillet on medium heat and swirl oil to coat. Add onion and bell pepper, saute for 3-4 minutes, stirring occasionally.
In a large slow cooker, add chicken breasts, sauteed onion and pepper, black beans and enchilada sauce. No need to stir.
Close the lid and cook on High heat for 3 hours or on Low heat for 5 hours.
Shred chicken with 2 forks right in slow cooker, then add corn tortillas and spinach. Stir gently to combine and sprinkle with cheese. Close the lid and let sit for 5 minutes for cheese to melt.
Garnish with your favorite toppings and serve warm by scooping with a spoon.
Notes
Store: Refrigerate covered for up to 3 – 4 days.
Freeze: Cool, transfer to an airtight container and freeze for up to 3 months. Thaw in the fridge overnight.