Trim tuna and remove dark parts. Cut in 2 x 2 inch (4 x 4 cm ).
Thread 2 or 3 pieces of tuna, alternating with the green onion pieces, in each skewer.
Brush tuna and onion with olive oil.
In a small saucepan, bring to a boil vinegar and sugar until it caramelizes. Add soy sauce, salt and pepper.
Cook skewers on the grill or grill pan 1 to 2 minutes per side or until they are golden. Brush with vinegar and soy sauce frequently. Tuna meat must be red in the center (medium rare).
Preparation Time: 30 minutes
How to fillet, skin and debone fish