Heat olive oil in a large skillet over medium heat.
Add minced garlic and diced onion, sauté until translucent.
Add ground chicken and cook until browned.
Stir in sliced bell pepper and chopped water chestnuts.
Pour in soy sauce, hoisin sauce, and rice vinegar; mix well.
Season with salt and pepper to taste.
Cook for an additional 2-3 minutes until everything is heated through.
Remove from heat and let cool slightly.
Separate lettuce leaves and wash them under cold water.
Spoon the chicken mixture into each leaf and add desired toppings.