Step 1

Hard boil the eggs using the stove top hard boiled eggs recipe or this instant pot hard boiled eggs recipe . Peel and thinly slice the eggs lengthwise.

Step 2

Halve the bread horizontally and scoop out about half the crumb from the top and a little less from the bottom half (so it doesn't fall apart when you eat it). Save the crumbs to make croutons or bread crumbs. Brush the insides of the bread with the olive oil.

Step 3

In a medium bowl, whisk together the vinegar and mustard. Season with pepper.

Step 4

Add the drained tuna, chopped olives, capers, and anchovies and gently fold into the dressing. Taste and add salt if necessary (it may not be, but the mixture should be well seasoned).

Step 5

Spoon the tuna mixture over the bottom half of the bread, all the way to the edges. Lay the sliced egg on top, followed by the cucumber slices, the tomatoes (season with salt and pepper if you like), the onion, and finally arugula leaves to cover the surface of the sandwich. Place the top of the sandwich over and press firmly.

Step 6

Wrap the sandwich tightly in plastic wrap. Put it on a plate to catch any potential drips, and transfer to the refrigerator. Place something heavy on top, like a sheet tray with a can of tomatoes on top; the more compressed it is, the easier it will be to eat. Refrigerate for at least one hour, or even better, up to overnight. When you're ready to serve, unwrap, and cut into six servings.