Step 1

Cook the potatoes: Bring a pot of salted water to a boil. Add the potatoes and boil until tender, 12 to 15 minutes. Drain, and when cool enough to handle, thinly slice.

Step 2

Make the chickpeas: While the potatoes cook, in a large bowl, combine the chickpeas, mayonnaise, lemon zest and juice, oil, garlic, salt and a big pinch of pepper. Using the back of a fork, mash the ingredients until you have a chunky but spreadable mixture. Taste, and season with more salt and/or lemon juice, if needed.

Step 3

Make the vinaigrette: In a small bowl, whisk together oil, capers, lemon juice, mustard, water and salt until combined.

Step 4

When ready to serve, set out 4 of the bread slices, divide the mashed chickpeas among them and spread in an even layer. Top with the tomato, cucumber, radish, olives, shallot or red onion and potatoes. Drizzle 1 to 2 tablespoons of the vinaigrette over the vegetables, lightly season with salt and black pepper, if desired, and top each sandwich with a piece of bread. Slice in half and serve.