Prepare ingredients by chopping vegetables and cutting chicken into uniform pieces.
In a small saucepan over medium heat, combine soy sauce, brown sugar, garlic, and ginger; stir until the sugar dissolves.
Heat oil in a skillet over medium-high heat; add chicken and cook until golden brown (5–7 minutes).
Add broccoli and bell peppers; stir-fry for an additional 3–5 minutes until veggies are tender yet crisp.
Pour teriyaki sauce over the chicken and vegetables; cook for another minute until well-coated.
Serve immediately over rice or quinoa and garnish with sesame seeds or green onions.
