Slice onion in rings, put in skillet with brown sugar. Cook over low heat until onions are clear. At the same time cut chicken into strips. After onions have been cooking for about 5 minutes but chicken in a separate skillet and cook on medium (may need to add a little oil so it doesn't stick). Add spices to chicken as it is cooking. When onions are done put in same pan as chicken and let them simmer together to a while. Put cheese on top of dish or serve separately. Heat tortillas and serve.