Chicken Meatball and Shishito Yakitori

Name: Chicken Meatball and Shishito Yakitori
Ingredients: 1/4 cup reduced-sodium soy sauce; 2 tablespoons mirin; 5 garlic cloves—2 crushed, 3 minced; One 2-inch piece of fresh ginger, thinly sliced, plus 1 1/2 tablespoons minced ginger; 1 teaspoon sugar; 4 white button mushrooms, chopped; 2 1/2 pounds skinless, boneless chicken thighs, chopped into 1/4-inch pieces; 1/4 cup plus 1 tablespoon shiro (white) miso; 2 tablespoons untoasted sesame oil or vegetable oil, plus more for brushing; 3 scallions, minced; 1/8 teaspoon kosher salt; 3/4 teaspoon freshly ground black pepper; 12 shishito peppers (see Note)