Steps
1. In a small bowl, combine soy sauce, mirin, sake, sugar, and grated ginger to make teriyaki sauce.
2. Season chicken thigh with salt and pepper.
3. Heat vegetable oil in a pan over medium heat. Add chicken and cook until browned on both sides.
4. Pour teriyaki sauce into the pan and simmer until the chicken is cooked through and sauce thickens.
5. In a separate pan, sauté bell peppers and shiitake mushrooms until tender.
6. Serve the chicken sliced over steamed rice, topped with sautéed vegetables and sesame seeds if desired.