Heat oil in pan and fry onions until limp. Add garlic and fy for 2 minutes. Remove onions and garlic, set aside. Add chicken to the now empty pan and stir fry for 2 minutes. Add soy sauce, ginger and mint leaves. Stir fry for 2 minutes. Add mushrooms, green onions, serranos and return garlic and onion to the pan. Cook for 5 minutes. Add rice vinegar, sugar, and fish sauce. Remove from heat and serve over rice.