Prepare the tuna mixture: In a bowl, mix the drained tuna and mayonnaise. Add salt and black pepper to taste.
Prepare the cucumbers: Dice the cucumbers into small pieces or slice them thinly, depending on your preference.
Combine the cucumbers: Add the diced cucumber into the tuna mixture, stirring until evenly combined.
Toast the bread: Toast the slices of bread to a golden brown, ensuring they’re not burnt.
Assemble the sandwich: Spread the tuna and cucumber mixture onto one slice of the toasted bread. If you haven’t diced the cucumbers, place the thinly sliced cucumbers on top of the tuna mixture.
Cover and serve: Place the second slice of toasted bread on top to complete your sandwich.