Mix together the dressing ingredients and season to taste. This makes a thick dressing.
Heat a griddle pan until hot. Brush the tuna with the oil and cook for 2 minutes per side for rare tuna, or for longer if you like it more cooked. Set the tuna aside to cool for a minute them slice.
Place the racket in a large bowl and top with the pieces of tuna. Spoon over the dressing just before serving.
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