Thoroughly wash the mushrooms and cut into quarters.
In a large skillet, heat the butter for 2 to 3 minutes over medium heat. Add the mushrooms. Saute until they are lightly brown and have begun to release their water, about 5 minutes.
In a small bowl, whisk together the miso, ginger, garlic, honey and hot water. Add the miso sauce to the mushrooms. Stir to coat. Simmer for another 5 to 8 minutes until the mushrooms are tender.
Stir in the green onion, sprinkle with sesame seeds, and serve.
