Asian Lettuce Wraps

• 1 tablespoon olive oil
• 1 pound ground chicken
• 2 cloves garlic, minced
• 1 onion, diced
• 1/4 cup hoisin sauce
• 2 tablespoons soy sauce
• 1 tablespoon rice wine vinegar
• 1 tablespoon freshly grated ginger
• 1 tablespoon Sriracha, optional
• 1 (8-ounce) can whole water chestnuts, drained and diced
• 2 green onions, thinly sliced
• Kosher salt and freshly ground black pepper, to taste
• 1 head butter lettuce