Use the sauté function on the Instant Pot or multifunction cooker to brown onion and garlic for 3 – 5 minutes using spray oil. Sprinkle in chili, oregano and sea salt & pepper as the onions brown. If needed, use a bit more oil spray to prevent burning. Alternatively, do the above steps in large pot with a heavy lid or Dutch oven.
Turn off the sauté function. Add the remaining ingredients EXCEPT the chocolate powder. Ensure that the chicken breasts are submerged in the liquid and stir to make sure the tortilla pieces are not stuck on the bottom. Pressure cook on HIGH for 15 minutes, or slow cook for 4 – 6 hours on HIGH (6 – 8 hours on LOW). Alternatively, add the ingredients to a Dutch oven set on low-medium heat, cover tightly and cook for 1 – 2 hours, checking often to ensure ingredients are not burning – adjust heat and add water/broth as needed.
After the cooking cycle has completed, release the pressure from the Instant Pot, remove the chicken and add to a separate bowl and shred with forks. Add cacao to the Instant Pot and use an immersion blender to blend the sauce. Alternatively, let the sauce cool down and add it to a blender, then add it back to the Instant Pot. Fold in the chicken and season to taste with sea salt & pepper.
Garnish and enjoy with a salad, tacos, burritos or my favorite, chocolate chicken quesadilla with a side salad.