
In a small bowl, stir together the hoisin, soy sauce, sweet chili sauce, rice vinegar, and toasted sesame oil. Set aside.
Heat the oil in a large skillet over medium heat. Add the chicken and cook, stirring to break into small crumbles, until browned, 6 to 8 minutes.
Add the onion, bell pepper, water chestnuts, ginger, and garlic. Cook, stirring often, until the vegetables are beginning to soften, about 8 minutes.
Stir in the sauce. Cook, stirring occasionally, until the vegetables are tender and the chicken is well covered in sauce, about 1 minute. Remove from heat.
Spoon about ¼ cup of the chicken mixture onto each lettuce leaf. Sprinkle the lettuce wraps with green onions and peanuts. Serve immediately.