in a small bowl, whisk together all sauce ingredients and set aside.
Heat sesame oil in a large high-sided skillet over medium-high heat. Season chicken thighs generously with garlic and onion powder and salt and pepper, tossing them in a large bowl to ensure every piece has seasoning. In two batches, cook chicken for 3-4 minutes. While chicken is cooking, steam broccoli until bright green and crisp.
Add broccoli to chicken and add rest of chicken to the pan, turn heat down to medium-low, then pour sauce into the pan. Stir well to coat everything, then allow to simmer until sauce thickens, about 2 minutes.
Serve over rice, then garnish with green onions and sesame seeds.