Prep the lettuce and veggies: Separate the lettuce leaves, rinse, and pat dry. Dice the onion, bell pepper, and mushrooms; grate the carrot; mince the garlic and ginger; slice the green onions.
Make the sauce: In a small bowl, whisk soy sauce, rice vinegar, hoisin, sesame oil, sriracha, and honey. Set aside.
Cook the aromatics: Heat oil in a large skillet over medium-high.
Add onion and the white parts of the green onions. Cook 2–3 minutes until softened. Stir in garlic and ginger for 30 seconds.
Brown the chicken: Add ground chicken.
Break it up with a spatula and cook until no longer pink, about 5–6 minutes. If there’s excess moisture, let it cook off for better texture.
Add the vegetables: Stir in mushrooms, bell pepper, and carrot. Cook 3–4 minutes until tender-crisp.
If using water chestnuts, add now.
Sauce it up: Pour the sauce over the mixture. Toss to coat and let it simmer 1–2 minutes to absorb and thicken slightly. Taste and adjust heat or sweetness if needed.
Finish and garnish: Remove from heat.
Stir in the green parts of the green onions and a handful of cilantro if using.
Assemble: Spoon the chicken filling into lettuce leaves. Top with sesame seeds and a squeeze of lime. Serve immediately.