1. Place lemon juice in small bowl. Whisk in 3/4 of the olive oil, then olive paste.
2. Sprinkle tuna with sea salt and black pepper; rub with remaining oil.
3. Heat heavy large skillet over high heat. Add tuna to skillet; sear on all sides, about 10
4. Transfer tuna to plate; chill 30 minutes.
5. Thinly slice tuna crosswise, reserving any scraps.
6. Spoon 1 tablespoon vinaigrette onto each plate. Arrange tuna slices, overlapping
slightly, in circle on each plate. Spoon remaining vinaigrette over tuna.
7. Dice any tuna scraps; place in center of circle.
8. Sprinkle with chives.