Coat inside of slow cooker with nonstick cooking spray.
Pre-heat broiler. Spray large baking sheet with non stick cooking spray. Arrange wings on prepared baking sheet. Broil 6 to 8 minutes or until browned, turning once. Transfer wings to slow cooker.
Combine hoisin sauce, 1/4 cup sriracha sauce and brown sugar in medium bowl; mix well. Pour sauce mixture over wings; stir to coat.
Cover; cook on low 3.5 to 4 hours. Remove wings to large serving platter; cover with foil to keep warm.
Turn slow cooker to HIGH. Cook, uncovered 10 to 15 minutes or until sauce thickens. Stir in remaining tablespoon of sriracha sauce. Spoon sauce over wings; sprinkle with green onions.