Prep the Components: Gently separate, wash, and pat dry 12 large outer leaves from the lettuce head. Set them aside to crisp up. On your cutting board, dice the shallot and red bell pepper, mince the garlic, grate the ginger, shred the carrot, chop the water chestnuts, and slice the scallions.
Whisk the Sauce: In a small bowl, whisk together the reduced-sodium tamari, maple syrup, rice vinegar, toasted sesame oil, and red pepper flakes.
Brown the Chicken: Heat a Dutch oven or wide sauté pan over medium-high heat with the avocado oil. Add the lean ground chicken. Break it apart with a spatula and cook for 5–7 minutes until fully browned and the internal temperature reaches 165°F (74°C).
Sauté Aromatics: Reduce heat to medium. Add the diced shallot, red bell pepper, and shredded carrot to the chicken. Sauté for 3–4 minutes until the vegetables soften. Stir in the minced garlic and grated ginger, cooking for another 60–90 seconds until fragrant.
Glaze the Mixture: Pour the prepared sauce over the chicken and vegetable mixture. Stir well to coat. Let the sauce bubble gently for 2–3 minutes. Watch closely as it reduces to coat the chicken without burning.
Add Crunch: Remove the pan from the heat. Fold in the chopped water chestnuts and sliced scallions immediately to preserve their crisp texture.
Assemble: Spoon approximately ⅓ cup of the filling into each lettuce leaf. Top evenly with toasted sesame seeds, chopped unsalted cashews, and extra scallions. Serve immediately.