Add diced onion and oil to large pan, cook over medium heat until softened

Add chicken breasts and cook in oil until chicken starting to brown

Add garlic and cook for 2 minutes, stir

Add tomatoes, chipotles and sauce, chicken stock, bay leaf, sugar, oregano and cumin

Cover, cook on low heat, just so sauce is simmering, cook for 45 minutes or until chicken starts to pry apart with a fork and knife

Break the chicken up a little and remove the lid, cook uncovered over low-medium heat until sauce disgnifcantly reduces into more of a thick gravy, rather than watery sauce

Continue gently shredding/brealking down chicken in pan as it cooks for desired final consistency