These colorful kebabs turn up at yakitori joints around Tokyo and make a terrific side dish or vegetarian appetizer.
Step 1: Cut the scallions crosswise into pieces the size of the mushroom caps, about 1-1/2 inches long. Thread the shiitake caps onto the skewers so they will lie flat on the grill, alter- nating them with pieces of scallion, threaded on crosswise. Place 3 mushroom caps and 4 scallion pieces on each skewer. Reserve any leftover scallion pieces for another use.
Step 2: Combine the soy sauce, mirin, sugar, and garlic in a small bowl and whisk until the sugar dissolves.
Step 3: Set up the grill for direct grilling and preheat to high.
Step 4: When ready to cook, brush and oil the grill grate. Arrange the kebabs on the hot grate with the aluminum foil shield under the ends of the skewers and grill, turning with tongs and brushing with the soy mixture, until the shiitakes are tender and the scallions are nicely browned, 3 to 5 minutes per side (6 to 10 in all). Serve at once.