Mix garlic, ginger, Ponzu Soy Sauce and mirin in a bowl and marinate tuna for about 10 minutes.
Drain (1) and wipe off excess marinade. Lightly coat tuna with corn starch.
Preheat the oil to 340-360℉ (170-180℃). Deep fry until golden brown.
Serve on a plate with lemon slices, if desired.
