Prepare Eggplant and Mushrooms: Slice the eggplants thickly and score one side in a diamond pattern. Cut the king oyster mushrooms into 4 pieces lengthwise.
Microwave Eggplant: Microwave the eggplant slices for 3 minutes.
Prepare Marinade: Mix soy sauce, shiitake mushroom soaking water, sugar, corn syrup, Korean cooking wine, minced garlic, sesame oil, and pepper in a bowl.
Marinate and Bake: Place the king oyster mushrooms on the microwaved eggplant slices, roll them, and stack in a heat-resistant container. Pour the marinade over them and let sit for 30 minutes. Bake in a preheated oven at 200ºC for 40 minutes.
Serve: Serve the eggplant galbi sprinkled with chopped green onion and sesame seeds.