In a medium bowl, toss the chicken with 1 tbsp. rice wine vinegar, the soy sauce and cornstarch. In a small bowl, mix the hoisin, ginger, 1 tbsp. rice wine vinegar and 2 tbsp. water.
In a large skillet, heat the sesame oil over medium-high. Add the onion and pepper; stir-fry 2 minutes. Add the chicken; stir-fry 2 to 3 minutes. Add the vegetables and sauce; stir-fry until the chicken is cooked through, 2 to 4 minutes. Top with nuts and scallions.