A Niçoise is only as good as its eggs and its potatoes. Boil the eggs for exactly 7 minutes so the yolks stay soft and jammy, and dress the potatoes while they are still warm, so they soak up the dressing instead of sitting on top of it.

A serving has about 46g of protein from the tuna and eggs, for around 550 calories. That makes it a lunch that keeps you going all afternoon, and a good one after training.
Tinned tuna is one of the cheapest lean proteins you can buy. Choose tuna in spring water rather than oil or brine if you are watching calories or salt. Note that the NHS does not count tuna, fresh or tinned, as an oily fish, as it is much lower in omega-3 fats than salmon or mackerel, so it does not count towards your weekly portion of oily fish.
The dressing matters. Extra virgin olive oil and olives provide mostly monounsaturated fat, and the fat helps you absorb the fat-soluble nutrients in the vegetables. The potatoes and green beans make it filling without bread.
Pregnant or trying to get pregnant? The NHS advises eating no more than 4 cans of tuna a week (about 140g drained each), because of mercury, and using British Lion eggs if you want the yolks soft. Otherwise, boil the eggs for 9 to 10 minutes.
Olives and anchovies are salty, so taste before adding more salt. For a heart-friendly way of eating around menopause, see menopause and heart health. For another tuna lunch, try the tuna, white bean and red onion salad.