Prepare the
barbecue (medium-high heat).
Grill the
baguette pieces, cut side down, until lightly toasted, about 2 minutes. Remove and set aside.
Combine the olives, capers, 1 tablespoon of oil,
lemon juice, parsley, lemon zest, and anchovy in a
food processor.
Pulse just until the olives are finely chopped. Season the
tapenade with salt and pepper.
Drizzle the tuna with the remaining oil. Sprinkle with salt and pepper. Grill the tuna until golden and seared on the outside, and just opaque in the center, about 2 minutes per side.
Stir the
mayonnaise and mustard in a small bowl to
blend. (The tapenade and Dijon-mayonnaise can be prepared 1 day ahead. Cover separately and refrigerate. Bring the tapenade to room temperature before using.)
Spread the Dijon-mayonnaise over the bottom and top halves of the baguette pieces. Top with red peppers and red onion. Cut the
tuna steaks across the grain into 1/2-inch thick slices. Arrange the tuna slices atop the
onions. Spoon the tapenade over the tuna. Top with the lettuce then the baguette tops, and serve.