Prepare an ice bath; set aside. Season tuna on both sides with salt and pepper.
Heat oil in a nonstick skillet over medium-high heat. Add tuna, and sear on both sides until the surface of the tuna becomes white, about 6 seconds per side. Plunge the tuna fillet into the ice bath to stop the cooking process. Drain, and shake to remove excess water.
Divide vegetables between 4 plates. Cut the tuna crosswise into 1/8-inch-thick slices. Roll each slice into a cylinder, and place them around the vegetables. Drizzle dressing between tuna rolls. Serve immediately.