Steps
1. In a small bowl, mix soy sauce, mirin, sugar, and sesame oil to create the teriyaki sauce.
2. Heat a non-stick skillet over medium heat and add a splash of oil.
3. Add sliced onions and sauté until translucent, about 3-4 minutes.
4. Push the onions to the side of the skillet and add the chicken pieces.
5. Season the chicken with salt and pepper and cook until no longer pink, about 5-6 minutes.
6. Pour the teriyaki sauce over the chicken and onions, cooking for an additional 2-3 minutes until the sauce thickens slightly.
7. Serve the chicken and onions over the cooked rice, garnished with chopped green onions if desired.