Slice zucchini on a mandoline to 1/4 inch thickness. Toss in marinade. This can be done two hours ahead of time.
Toss grape tomatoes in olive oil and place under a hot broiler until blistered.
Spread the Tonnato on the plate in a thin layer. Drain excess marinade from zucchini and season to taste with salt. Plate zucchini on top of the Tonnato.
Garnish with the blistered tomato, parsley leaves and chives or scallions.
For the Tonnato:
Gather all ingredients.
Drain oil from Tuna.
Place all ingredients in a food processor and chop until all ingredients are chopped fine.
For the Zucchini Marinade:
Place all ingredients in a blender with the exception of the oil.
Blend until liquified.
With the blender on its highest speed, slowly drizzle in the oil.