Brown chicken in oil, till golden brown on both sides.Place onions on top of chicken and add margarita mix reduce heat cover and simmer for about 5-10 minutes. Check chicken if there is just a hint of pink remove it to a serving platter along with the onions and cover with foil. You don't want to overcook the chicken. The heat in the chicken will continue to cook the chicken. Turn heat up and reduce sauce to a pancake syrup consistency. Pour Sauce over chicken and serve.