(Marinade) In a small bowl, stir together soy sauce, garlic, sugar, and ginger.
Place fish in a resealable plastic bag, pour in marinade, seal and set in a shallow dish in the refrigerator.
Marinate for 1 to 2 hours turning bag occasionally. Drain and discard marinade just prior to grilling the tuna.
Grilling: a) For a charcoal grill, grill the fish on a greased rack of an uncovered grill over medium coals to 8 to 12 minutes (fish should flake easily... don't over cook or it will get tough) turning once. b) For a gas grill, preheat the grill, reduce heat to medium, place fish on grease grill rack, cover and grill as above.
After grilling the tuna, cut it into 1/2 inch chunks.
Brush both side of tortillas lightly with olive oil and grill for 30 to 45 seconds or until warm.
In a medium bowl, stir together the sour cream and salad dressing.
For each wrap, spread 3 Tbsp of the sour cream mixture on the tortilla.
Place some tuna near an edge of the tortilla
Top with arugula, onion, and tomato.
Fold edge over filling, fold in the sides and roll up