Place chicken breast in a slow cooker and season with salt and pepper, garlic powder and cumin.
Toss in chopped onion, bell pepper, jalapeños and cilantro.
Pour in salsa, spreading it to cover all the chicken. Place the lid over the slow cooker and set it to high. Let it cook for 4 hours.
After 4 hours, shred chicken using two forks then mix in cream cheese or sour cream.
Either continue the next steps in the slow cooker or preheat the oven to 350F and transfer the mixture to a baking dish for faster results and a darker top.
Chop corn tortillas into squares (about an inch) then add them to the mixture. Spread them evenly all around making sure they are completely covered in sauce.
Add about a cup of cheese mixing it in as well then top the mixture with the remaining cheese.
If continuing in the slow cooker, place the lid back on and let it continue to cook on high for another 30 to 40 minutes. If continuing in the oven, bake for about 15 to 20 minutes or until cheese is melted and darkened to your liking.