Make the sauce: In a small bowl, whisk soy sauce, honey, rice vinegar, mirin, sesame oil, water, and sriracha.
Set aside. In a separate small cup, stir together cornstarch and water to make a slurry.
Prep the lettuce and veggies: Separate lettuce leaves, rinse, and pat dry. Chop bell pepper, shred carrots, and slice green onions.
Keep the crunchy add-ins nearby.
Cook the chicken: Heat oil in a large skillet over medium-high. Add chicken and cook, breaking it up if ground, until no longer pink and lightly browned at the edges, about 5–7 minutes. Season lightly with salt and pepper if desired.
Add aromatics and veggies: Stir in garlic and ginger.
Cook 30–60 seconds until fragrant. Add bell pepper and water chestnuts (if using). Cook 2–3 minutes until just tender but still crisp.
Sauce it up: Pour in the teriyaki sauce.
Bring to a simmer, then stir in the cornstarch slurry. Cook 1–2 minutes until glossy and thick enough to coat the chicken. If it gets too thick, add a splash of water or broth.
Finish and taste: Stir in half the green onions.
Taste and adjust: add a pinch more honey for sweetness, vinegar for brightness, or sriracha for heat.
Assemble: Spoon the teriyaki chicken into lettuce leaves. Top with carrots, remaining green onions, and sesame seeds. Add optional cucumbers or a squeeze of lime.
Serve right away: Lettuce wraps are best enjoyed immediately while crisp and juicy.