Dice the onion, garlic, and water chestnuts (if not pre-diced). Grate the ginger and slice the scallions.
Heat a large skillet over medium-high heat. Add both oils, and when nearly smoking, add chicken. Cook until chicken is browned, about 5-8 minutes. Remove any excess liquid.
Add onion, soy sauce, rice wine vinegar, sriracha, and hoisin sauce. Cook, stirring occasionally about 3 minutes. Add the garlic and cook another 2 minutes or until onion is softened.
Add water chestnuts and scallions and cook another 2 minutes. Adjust flavoring as you want.
Serve 1/4 cup of chicken mixture inside each lettuce cup.