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But especially when it comes to salade niçoise preserved tuna is the only correct choice, whether it is packed in a can, a jar or a ceramic jug. Because of its oil-softened crumbliness and intense salinity, preserved tuna enlivens the olive-oil and vinegar dressing as well as the other traditional ingredients: sliced boiled potatoes, cooked green beans, black olives, hard-boiled eggs and tomatoes. For added salty intensity, capers and/or anchovies are often included. Cucumber and artichokes are also considered acceptable but leafy greens definitely are not, no matter how strongly they say salad to so many.