Prep your produce. Wash and separate the lettuce leaves. Mince the garlic and grate the ginger. Slice the green onions, reserving the greens for topping.
Dice the red bell pepper and water chestnuts if using.
Make the sauce. In a small bowl, whisk together sweet chili sauce, soy sauce, rice vinegar, and lime juice. Set aside.
Heat the pan. Add the neutral oil to a large skillet over medium-high heat. When it shimmers, add the white parts of the green onions, garlic, and ginger.
Cook for 30-45 seconds until fragrant.
Brown the chicken. Add the ground chicken and break it up with a spatula. Cook for 5-7 minutes until no longer pink and lightly browned in spots. Season with a small pinch of salt if desired.
Add veggies. Stir in the diced red bell pepper and water chestnuts.
Cook for 2-3 minutes to soften slightly while keeping some crunch.
Sauce it up. Pour the sauce into the skillet. Stir to coat the chicken evenly. Let it bubble for 2-3 minutes until slightly thickened and glossy.
Finish with sesame oil. Turn off the heat and stir in the sesame oil.
Taste and adjust: add more lime for brightness, a splash of soy for salt, or a touch more sweet chili for sweetness.
Assemble. Spoon the chicken mixture into lettuce cups. Top with green onion tops, cilantro, sesame seeds, peanuts, and a pinch of red pepper flakes or a drizzle of sriracha if you want heat.
Serve immediately. These are best eaten fresh so the lettuce stays crisp and the filling stays warm.