In a small bowl combine miso paste, soy sauce, Mirin, sugar, and chopped garlic. Whisk together until mixture is well blended. Pour marinade over chicken and allow chicken to soak up marinade for at least 30 minutes. Preheat oven to 350 degrees. Place marinaded chicken into a baking dish. Bake chicken for 25 minutes or until chicken is done, it is done when the chicken is pierced and the juice runs clear.
Serve with cooked rice if desired.