Preheat the grill to medium-high.
Rub the tuna on all sides with the oil and lightly season with salt, pepper and the herbs. Grill, turning, until medium-rare. Remove and let rest for 5 minutes. Thinly slice.
With a fork, scrape out the inner crumbs from both halves of bread. Spread both sides of each roll with tapenade. On the bottom slices of bread, layer the tomatoes and onions over the tapenade and top with other ingredients.
Yield: 4 servings