In a small bowl, combine the miso paste, soy sauce, mirin, sugar, and chopped garlic. Whisk until well blended. Pour the mixture over the chicken and marinate for at least 30 minutes.
Preheat the oven to 350°F.
Remove the chicken from the marinade and place it in a baking dish. Discard the marinade.
Bake for 25 minutes, or until the chicken is cooked through. The chicken is done when it reaches an internal temperature of 165°F.