Preheat a grill to medium high and brush the grates with vegetable oil. Combine 2 tablespoons vegetable oil, the soy sauce, ginger, five-spice powder and white pepper in a large bowl. Add the chicken and toss to coat. Thread the chicken onto four 10-inch skewers. Thread the peppers and bok choy onto 4 more skewers.
Grill the chicken, covered, turning occasionally, until well marked, 10 to 12 minutes, brushing with the hoisin sauce during the last minute of grilling. Sprinkle with sesame seeds and scallions.
Meanwhile, brush the vegetable kebabs with vegetable oil and season with salt. Grill until the vegetables are charred, about 3 minutes per side. Serve with the chicken kebabs.