Place the chicken in a bowl and add the oregano, cumin, salt, sugar, 1 tablespoon of the garlic oil (crushed garlic if you don't have garlic oil) and 1 tablespoon of the lime juice. Toss the chicken until it is well coated in the mixture and leave it to marinate.
Heat the oil in a large pan, add the onions to pan and stirring occasionally, cook until the onions have softened. Add the capsicum to the pan and cook until they have softened. Remove the onions and capsicum to a bowl.
Heat the rest of the garlic oil (regular olive oil if you don't have garlic oil) in the pan and add the chicken and its marinade.
Cook the chicken, stirring, until it is sealed and almost cooked through then return the onions and capsicums to the pan. Keep cooking, while stirring, until the capsicum and onions are hot and the chicken is cooked through. Tip the contents of the pan into a serving dish and cover to keep warm.
Warm the tortillas in the oven or microwave and serve the meat, tortillas and accompaniments on the table for everyone to help themselves.