The recipe I have from Claudia Roden's Mediterranean Cooking uses baguette. But Provence is close to the Italian border (which has moved around a bit over the centuries), and I would not be surprised if it has been made with what I was brought up in Italy calling Pane Genovese (Genoese bread), and what everybody else now calls focaccia.
Serves 1 hungry person
1 piece of focaccia, roughly 20cm x 15cm or a 20cm length of baguette
1 small garlic clove, crush or thinly sliced
1 tomato, thinly sliced
2-3 slices hard boiled egg (optional)
4-5 black olives (optional)
2-3 anchovy fillets (optional)
A few cucumber slices
2-3 slices of sweet bell pepper, any colour
Sprinkling of chopped onion or spring onion
A few drops of vinegar
A drizzle of olive oil
A few sprigs of basil, parsley or thyme (optional)
Pepper and salt
As you will see from how many things I have marked as optional, this sandwich filling is quite literally a very moveable feast. I don't like egg, and anyway would never have a boiled one floating around waiting for a use. I do love anchovies and olives, but only had anchovies on the day I made it. To me, essentially, the key ingredients are the garlic, tomato, bell pepper, onion, oil & vinegar, seasoning and herbs (if you have some) for a little taste of the Mediterranean.
Take your baguette or focaccia and carefully slice it down the side to open it up. If using baguette squash both halves of the bread flat with the palm of your hand to make the surface as flat and as wide as you can.
Drizzle the oil on all the open sides of the bread, lay the tomato on first (you want these juices in particular to soak into the bread). Lightly season with salt & pepper and then continue layering in your filling, lightly seasoning as you go as the salt will draw out the lovely flavoured juices of your salad ingredients.
When filled, press the 'lid' of your sandwich down firmly and wrap tightly in cling film. Ideally this sandwich is best made the night before or first thing in the morning to be eaten at lunchtime. Then the juices will have mingled together soaking into the bread. But even a 10 minute wait is sufficient. Even avid meat eaters may be surprised how filling this sandwich is!