Roughly chop the anchovies, capers and mince garlic, then add them to a mortar with a pinch of coarse salt and turn them into a paste. Alternatively you can use a blender.
In a mason jar combine extra virgin olive oil, red wine vinegar and the anchovy, caper, garlic paste with a whisk or a fork.
For the tuna salad
In a large salad bowl combine all ingredients and drizzle with the vinaigrette. Alternatively you can arrange ingredients on top of lettuce leaves, then drizzle with vinaigrette and let your guests help themselves.