In a medium bowl, combine all "Marinade" ingredients and stir until sugar is dissolved.
Add chicken to a large ziplock bag, or lay it on a very lightly oiled baking dish.
Top the chicken with the marinade.
If you are using a ziplock bag, close it and place it in the fridge. If you are using a baking dish, cover it with plastic wrap and transfer it to the fridge.
Marinate the chicken for 1-8 hours, make sure you flip it at least once during this time so it marinates evenly.
If you used a baking dish, remove it from fridge and let it stay at room temperature for one hour, before placing it into the hot oven. If you used a ziplock bag, 30-40 minutes at room temperature would be enough.
Preheat oven to 425 degrees F.
If you used a ziplock bag, add chicken to the baking dish and top it with the marinade.
Add the halved onions to the baking dish.
Baked uncovered in the hot oven for 15-18 minutes, or until the chicken is cooked through and no longer pink. If you use a cooking thermometer, the temperature in the thickest part of the breast, should be between 165-170 degrees F.
Using a baster or spoon, pour the sauce mixture over the chicken 1 or 2 times while baking.
For a crispy, brown top, turn the broiler on high for the final 5 minutes and broil the chicken until it is cooked through and extra browned on top. Watch it closely, so that it does not overcook and/or burn.
Once the chicken is cooked, remove the pan from the oven and loosely cover the pan with aluminum foil. Let the chicken rest for at least 5-10 minutes.
Slice the chicken and top it with a few spoons of sauce from the pan. Then serve immediately with rice and steamed veggies.
Garnish with green onions and sesame seeds.
The chicken can be refrigerate in a sealed container for up to 3 days, or freeze for up to 3 months.