In a large skillet, combine salsa, green onions and 2 tablespoons Hidden Valley® Original Ranch® Seasoning & Salad Dressing Mix Shaker. Cook, uncovered, over medium heat until heated through, about 10 minutes, stirring occasionally.
Brush 1 side of tortillas with butter; place buttered side down on a lightly greased baking sheet. Spoon 3/4 cup chicken mixture over half of each tortilla; sprinkle with 1/3 cup cheese.
Fold plain side of tortilla over cheese. Bake at 375° until crisp and golden brown, 9-11 minutes.
Meanwhile, stir together sour cream and remaining 1 tablespoon Hidden Valley® Original Ranch® Seasoning & Salad Dressing Mix Shaker. Cut quesadilla into wedges; serve with ranch sour cream.