1In a small bowl, whisk together soy sauce, rice vinegar, honey, sesame oil, water, and cornstarch until smooth. Set aside.
2Heat 1 tbsp vegetable oil in a wok or large skillet over medium-high heat. Working in two batches, cook chicken until golden and cooked through, about 4–5 minutes per batch. Transfer to a plate.
3Add remaining 1 tbsp oil to the wok. Add onion and bell pepper; stir-fry for 2–3 minutes until just tender-crisp.
4Add garlic, ginger, and red pepper flakes; cook for 30 seconds until fragrant.
5Return chicken to the wok. Pour in sauce and toss until everything is coated and the sauce thickens, about 1–2 minutes.
6Stir in peanuts and most of the green onion. Taste and adjust seasoning as needed.
7Serve over steamed rice or noodles. Garnish with remaining green onion.