lettuce wrap recipe

1 pound ground chicken or turkey - 1 tablespoon vegetable oil - 1 small onion, finely chopped - 3 cloves garlic, minced - 1 tablespoon fresh ginger, minced - 1/4 cup hoisin sauce - 2 tablespoons soy sauce - 1 tablespoon rice vinegar - 1 tablespoon sriracha or chili sauce (optional, for heat) - 1 can (8 ounces) water chestnuts, drained and chopped - 2 green onions, chopped - 1/4 cup fresh cilantro, chopped (optional)