Step 1

In a small bowl, whisk together vinegar, tarragon, mustard, shallot, salt and pepper.

Step 2

Slowly whisk in oil to make a vinaigrette.

Step 3

Put tuna into a wide, shallow dish, and drizzle all over with 2 tablespoons of the vinaigrette.

Step 4

Cover and chill for 30 minutes.

Step 5

Reserve remaining vinaigrette.

Step 6

Prepare a grill for medium heat cooking.

Step 7

Arrange tuna on the grill and cook 5 to 7 minutes on each side, or until tuna reaches desired doneness. Transfer to a plate.

Step 8

When cool enough to handle, flake into large pieces.

Step 9

Arrange tuna, potatoes, green beans, tomatoes, olives, onion and egg on a large platter and serve with reserved vinaigrette on the side to spoon over the top.