Heat the butter in a sauce pan over medium heat until melted, add the garlic, shallot and green onion and sauté for 30 seconds until fragrant
Add in the miso, soy sauce, sake, chicken broth and oyster sauce and stir for 30 seconds
Allow to cool for 10 minutes
Transfer to a medium bowl
Add the mushrooms and allow to marinate for 30 minutes
Skewer the mushrooms and grill over medium-high heat until just tender and slightly charred, about 2-3 minutes per side
Brush with remaining marinade occasionally while mushrooms cook
Garnish with more green onions and serve immediately