Cut fennel bulbs vertically into 1/2-inch slices. Blanch fennel in boiling water 3 minutes or just until crisp-tender; drain. Combine fennel and radicchio in a large bowl; set aside.
Combine orange juice and next 6 ingredients in a jar. Cover tightly, and shake vigorously. Chill 1/4 cup vinaigrette; pour remaining vinaigrette over fennel and radicchio, tossing gently to coat. Let fennel mixture stand 15 minutes; drain.
Grill fennel, covered with grill lid, over medium-hot coals (350° to 400°) 15 minutes, turning once. Remove fennel from grill, and set aside. Grill radicchio, covered with grill lid, 2 minutes or until crisp-tender. Toss fennel and radicchio with reserved vinaigrette; garnish, if desired. Serve immediately.
Note: Don't core fennel before grilling. The core will hold the slices of fennel together so they won't fall through the grill rack.