In medium bowl, whisk sour cream and seasoning; fold in chicken, cheeses and onions. Makes about 1 1/2 cups chicken mixture.
Leaving a 1-inch border, spread chicken mixture over tortillas; tightly roll up tortillas to enclose filling. Tightly wrap roll-ups in plastic wrap; refrigerate at least 2 hours or up to overnight.
Remove plastic wrap from roll-ups; trim 3/4-inch from each end. Cut each roll-up crosswise into 8 (3/4-inch-thick) slices. Makes 24 pinwheels.