Heat vegetable oil in a large skillet or wok over medium-high heat.
Add the ground chicken and cook until browned, breaking it into small crumbles with a spatula.
Add the diced onion and sauté for 2 minutes until softened.
Stir in the garlic, ginger, and water chestnuts, cooking for 1 minute until fragrant.
In a small bowl, whisk together hoisin sauce, soy sauce, rice vinegar, sesame oil, and sriracha.
Pour the sauce over the chicken mixture and stir to combine.
Cook for 1-2 minutes until the sauce has thickened and the chicken is thoroughly glazed.
Remove from heat and garnish with sliced green onions.
Spoon the chicken mixture into the prepared lettuce leaves and serve immediately.