PLACE half the radicchio leaves in single layer in sheet pan. Roast in 350ºF convection oven 10 min. or until crisp. Cool.
DRESSING: WHISK mustard and vinegar until blended. Gradually add oil, whisking constantly until blended.
SALAD: COMBINE ingredients. Add Dressing; mix lightly.
FOR each serving: Line 1 roasted radicchio with unroasted radicchio leaf; fill with 1-1/4 cups Salad.