Preparation Heat heavy small skillet over high heat 2 minutes. Brush tuna with 1/2 tablespoon oil; sprinkle with salt and pepper. Place in skillet and sear until brown outside and almost opaque in center, about 3 minutes per side. Cool tuna; dice finely. Combine tuna, remaining 3 tablespoons oil, and all remaining ingredients in medium bowl. Using fork, mix just to blend. Season tartare to taste with salt and pepper and chill.
Preparation Heat heavy small skillet over high heat 2 minutes. Brush tuna with 1/2 tablespoon oil; sprinkle with salt and pepper. Place in skillet and sear until brown outside and almost opaque in center, about 3 minutes per side. Cool tuna; dice finely. Combine tuna, remaining 3 tablespoons oil, and all remaining ingredients in medium bowl. Using fork, mix just to blend. Season tartare to taste with salt and pepper and chill.