In a medium bowl, whisk together the soy sauce, honey, rice vinegar, sesame oil, ginger, and garlic until well combined.
In a large skillet, heat a splash of olive oil over medium-high heat. Add the diced chicken thighs and season with salt and pepper.
Cook the chicken for about 5-7 minutes until browned and cooked through, stirring occasionally.
Pour the teriyaki sauce mixture over the cooked chicken. Cook for an additional 3-4 minutes, stirring constantly, until the sauce thickens slightly and coats the chicken evenly.
Stir in the diced bell pepper and sliced green onions, cooking for another 2 minutes until the peppers are slightly tender but still crisp.
Remove from heat and let the mixture cool slightly.
To serve, spoon a generous portion of the teriyaki chicken mixture into each lettuce leaf.
Garnish with additional green onions and sprinkle with black sesame seeds if desired.