Preheat oven to 400°F (200°C). Line your sheet pan with parchment or foil for easier cleanup.
Make the sauce: In a mixing bowl, whisk together soy sauce, hoisin sauce, honey, rice vinegar, sesame oil, garlic, ginger, and red pepper flakes. Set aside.
Toss the chicken: In a large bowl, combine chicken cubes with half of the sauce and 1 tablespoon olive oil. Let it marinate while you prep the vegetables.
Prep the veggies: Toss bell peppers and red onion with remaining olive oil and a pinch of salt and pepper.
Assemble the sheet pan: Spread chicken pieces evenly on the pan, followed by the veggies. Bake for 15 minutes.
Add the cashews: After 15 minutes, scatter cashews over the pan and drizzle everything with the remaining sauce.
Roast until golden: Continue baking for another 8–10 minutes, or until chicken is cooked through and slightly caramelized.
Garnish and serve: Top with chopped green onions and sesame seeds, and serve over hot rice if desired.