Prepare barbecue (medium-high heat). Blend Wasabi Mustard in medium bowl with chives, sherry and ginger. Add fish; stir gently to coat. Let stand at room temperature 15 minutes. Brush fish rack with oil. Thread fish on skewers alternately with squares of bell pepper. Sprinkle with salt and pepper. Grill until fish is just opaque in centre and peppers are slightly charred, turning occasionally, about 8 minutes. Serve with thinly sliced cucumber tossed in a dressing of rice vinegar and vegetable oil. Serve with extra wasabi mustard on the side.