The ingredients you listed have the makings of a vinegarette. Add some chile for heat, a little soy for flavor, a touch of sesame oil, and whisk together with canola to emulsify. That will thicken your sauce. Sear your ahi to rare then use the sauce for dipping. You don't have to cook the sauce. With the ginger, if you have a microplane or similar type small grater, use that.
"Boldness has genius, power, and magic in it."
Johann Wolfgang Von Goethe