Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain bacon slices on paper towels, reserving grease in skillet.
Add chicken to skillet and stir to coat with bacon drippings. Season with salt and pepper.
Mash avocado in a bowl and season with lemon juice, garlic, salt, and pepper. Add tomato and onion to taste.
Divide cooked bacon, chicken, and avocado spread between lettuce leaves and wrap up.