Preheat oven to 425 degrees F. Spray a large baking dish (about 9 x 13 inches) with cooking spray and set aside.
Place diced chicken in a large Ziploc bag. Sprinkle the cornstarch into the bag, seal the bag, and toss to coat the chicken pieces.
Dump chicken into the prepared baking dish. Add cabbage and mushrooms, toss to combine.
In a separate bowl, whisk together brown sugar, soy sauce, hoisin sauce, rice vinegar, sesame oil, salt, garlic, and ginger. Pour sauce into dish and stir.
Bake, uncovered, for a total of 30 minutes, stirring twice during the cooking time. Remove from the oven with the chicken is cooked through and the sauce has thickened.
Season with additional salt and pepper, to taste. Garnish with sliced green onions, sesame seeds, and an extra drizzle of hoisin sauce, if desired. Serve with tortillas, rice, lettuce wraps or cauliflower rice.