in a medium bowl, whisk together hoisin, soy sauce, sesame oil, ginger, and garlic until combined. set aside.
in a large bowl, add chicken, bok choy, and scallions. drizzle oil, season thoroughly with salt and pepper, and toss to coat.
preheat grill to medium-high for 3 minutes. if you’re using wood skewers, soak them in a shallow pan filled with water for 10 minutes to prevent scorching. once soaked, thread chicken, bok choy, and groups of 3 scallions onto skewers.
transfer skewers to the grill and cook for about 4 minutes, flipping occasionally. after the first 4 minutes, begin brushing the skewers with the hoisin mixture after each flip. cook for an additional 4 to 5 minutes, or until the thickest piece of chicken reaches 165ºF on thermometer.
transfer to a platter, sprinkle on sesame seeds and serve.