Trim broccoli; cut flowers and stems into about 20 three to four inch long pieces. Cook in boiling salted water about 5 minutes or until tender; drain. While hot sprinkle with cheese. Spread one side of chicken slices with a combination of mayonnaise, yogurt and mustard. Place one length of cooked broccoli in center of each chicken slice. Roll up like a conucopia with broccoli flower protruding through the open end. Serve warm or cold.