Here are the ingredients for salade nicoise, which we had for dinner recently. The eggs and vegetables were from the farmers market; though I don't think of it as a seasonal dish, of course it's better when the vegetables are in season.
I can't remember whether I saw this dish in France prior to making it from Mastering the Art of French Cooking (p. 542, except I leave out the anchovies). I distinctly recall eating the potato component (pommes a l'huile, p. 541) in the incredibly cheap restautrants where we sometimes ate on our first trip to France, but if I remember correctly, they were usually served as an appetizer with one small fish filet like an anchovy or herring.
At various times, salade nicoise has been trendy on both sides of the Atlantic. On this side of the ocean, there's a tendency to upscale the dish by using fresh tuna. This is probably closer to the original version served in Nice -- after all, that's a fishing port famous for fresh Mediterranean seafood. Fresh Mediterranean tuna is something to dream about.
In the less expensive types of French casual dining places, it can actually be pretty bad. I have been especially disappointed when I find rice instead of the potato salad, or find canned green beans or even canned corn instead of what I think of as the classic ingredients.
Julia Child's version is what I've internalized -- as I've mentioned, I make a number of her recipes without looking in the book, and this is one of them. There are many variations in other cookbooks. In La Cuisine pour Tous, Ginette Mathiot almost agrees with Julia Child: she adds bell pepper (which I also do). The Larousse Gastronomiqe mentions ONLY anchovies, not tuna at all. Mireille Johnston's Provencal/Nicoise cookbook The Cuisine of the Sun lists every Mediterranean vegetable you can think of. Raymond Olivier, in La Cusine (a French classic) lists the ingredients as rice, carrots, onions, eggs, anchovies, tomatoes, herrings, sweet and hot peppers, and green and black olives. Really different!