Spray 3 1/2- to 4-quart slow cooker with cooking spray. Place chicken in cooker. Pour Buffalo wing sauce over chicken. Cover; cook on Low heat setting 6 to 7 hours.
Remove chicken from cooker; place in medium bowl. Place strainer over another medium bowl. Strain juices from cooker; skim fat from juices. Reserve 1 1/2 cups juices. Stir chicken to separate into pieces. Return chicken to cooker; stir in reserved juices. Increase heat setting to High. Cover; cook about 15 minutes or until thoroughly heated.
Spoon about 1/4 cup chicken mixture onto center of each lettuce leaf. Top with blue cheese; garnish with green onions and peanuts. To eat, wrap lettuce around chicken mixture and toppings.