Combine the miso, sake, mirin, maple syrup, sesame oil and ginger. Stir to combine.
Pour the marinade over the chicken and refrigerate at least one hour. You can go up to 8 hours. There is no acid in the marinade so there's no issue with the chicken cooking (think ceviche). Reserve the marinade when you are done marinating the chicken. Don't throw it out. This is important.
Pre-heat your oven to 375F.
Remove the chicken from the marinade and place into a dish that can go from the oven to the stove-top. You don't want a pan that is much bigger than the chicken. A frying pan with heat resistant handles is great for this.
Roast until the internal temperature of the chicken reaches 160F. Remove the chicken from the pan and set aside.
Place the frying pan (or whatever you are using) over medium heat. When it starts to bubble stir up any browned bits in the pan. Add the reserved marinade and bring to a lively simmer. This kills any bacteria so make sure you see bubbles in the pan.
If your sauce seems dry add a little drizzle of chicken stock. You don't get a lot of sauce here. It's just a drizzle so don't go crazy.
To serve, slice the chicken and drizzle the sauce overtop. Garnish with sesame seeds and chives or green onions.