Trim the end root of the enoki mushroom to where the little mushrooms can be separated individually, then set aside.
Whisk together soy sauce, oyster sauce, mirin, sesame oil, and sugar in a bowl. Marinate chicken thighs for 14 mins in this, 7 mins on one side and 7 on the other.
While the chicken is marinating, peel the ginger and mince both the garlic and ginger.
Heat olive oil in a skillet over med-high heat. Add in the minced garlic and ginger and cook until fragrant for 1 minute.
Add the chicken to the skillet, with about a tablespoon or 2 of the marinade. Cook each side for about 5-7 minutes, or until the chicken is fully cooked and golden brown. Then remove with tongs from skillet and set aside wrapped in tin foil.
Add more olive oil in the same skillet, then the enoki mushrooms and a little more marinade, and saute for 2-3 minutes until they are tender. Season with a pinch of salt and pepper.
Return the chicken (and the juices from the chicken) to the skillet with the mushrooms and gently push them around together. Cook combined for another 1-2 minutes to combine flavors.
Serve on rice, and garnish with sesame seeds and green onions (optional).
