Wash the cucumber and eggs thoroughly.
Boil the eggs, let them cool, then peel off the shells.
Cut the cucumber in half and slice thinly, then mash the boiled eggs finely.
Drain the oil from the canned tuna and set aside.
In a bowl, combine cucumber, boiled eggs, and tuna. Add mayonnaise and salt, and mix well.
Serve the salad on a plate and sprinkle with pepper to taste.