ASTUCES: if you us tuna in the salade, use either canned albacore, or the quantity of fresh tuna you like. i suggest 12 ounces; 400g. Sear the whole fresh piece first on each side, season with salt and pepper and let cool. Then, thinly slice the seared tuna and arrange it atop the salad after you’ve tossed the other ingredients together. Don’t use anchovies if you’re using tuna.
When the galette is fully cooked on one side, flipped and just about cooked on the other side, you can add the filling, spreading it out as you like, then fold the galette up to the center of the filling, as in the photo.