Pan Bagnat

This is a fantastic sandwich which originates from Nice, France.  From Food & Drink 2011

1 cup sweet white onion, very thinly sliced into rings
1/4 cup white wine vinegar
Salt
4 cans (198g each) Tuna in oil, drained
1/3 cup good quality olive oil, plus more for drizzling
1/4 cup capers, drained
1/2 cup fresh basil, coarsely chopped
Freshly ground pepper
2 baguettes
10 leaves Boston Lettuce, washed
12 slices tomato
4 eggs, hard boiled, peeled and sliced
1/2 cup brine cured black olives, coarsely chopped

1. Place in a medium bowl onion, vinegar and sprinkle of salt (I omit the salt).  Stir and let rest 5 minutes. Add tuna, olive oil, capers and basil.  Season generously with salt and pepper.  Stir together while breaking the tuna into small pieces. 
2. Slice baguettes in half lengthwise.  Remove the bread from the inside of the bottom halves of the loaves to form a gully.
3. Place the lettuce on the bottom halves of the loaves.  Place tuna mixture on top of lettuce and then tomato and egg slices on top of tuna.  The tuna mixture may be quite runny.
4. Sprinkle with olives.   Drizzle with olive oil and cover with top of baguette.  Slice each baguette into 4 pieces.