How to do it:

Cut off the dome of the king oyster or trumpet mushrooms and set aside now slice the stems in half. Score, diagonally, the king oyster mushroom several times on both sides without cutting it apart. This will allow your seasoning to go throughout the mushroom(s). Marinate your mushroom(s) for at least 1 hour covered. 

Warm up your sesame oil, in a cast iron grill skillet and add your onion flakes and kelp for shrooms. When adding your king mushroom(s) to the oil you should hear a searing sound to let you know it's hot enough. Place flat side of mushroom(s) down into grill skillet. After a few seconds smash down on mushrooms so it releases its water and juices. Tilt your skillet so juices run to one side and flip your mushroom(s) to sear the other side. You'll smash down the mushroom(s) several times as this juice and oil will be used to base your mushroom(s) after searing on both sides. Continue to baste, smash, and sear for at least 10 minutes to cook mushroom(s) thoroughly.