For this sandwich or any recipe where tuna isn't doused in mayo or baked with noodles, it's worth splurging on a high-quality, imported brand. (One we love: Conservas Ortiz, a Spanish tuna available at specialty stores such as Whole Foods or online.) This kind of tuna is line-caught, delicately poached and hand-packed in olive oil so it stays firm and flakes beautifully. The oil keeps the fish moist and silky and adds a rich, almost buttery flavor. You could even use the olive oil from the can to bathe your bread in Step 1 of the recipe---it's that good.
White anchovies are more mild in flavor than regular canned anchovies, but if you're not a fan, just skip them.
Drain and rinse one 15-ounce can chickpeas. Mash slightly. Thinly slice 1 bulb fennel, removing the woody core. Compose the sandwich as follows: potatoes, cucumber, chickpeas, lemon juice, tomato, eggs (omit for a vegan choice), sliced fennel, olives and capers. Continue as directed in Step 3.