Chop onion and bell peppers into large chunks. Place chicken breasts at bottom of pot (if breasts are unusually thick and large cut them in half first). Sprinkle meat with taco seasoning and cumin.
Put onion and bell peppers on top of meat, then pour jar of salsa on top of everything.
Cover and cook on low heat for 6 hours. Shred meat, stir, and serve inside tortillas with sour cream and cheese!