Prepare the Potatoes: Wash and peel the potatoes, then cut them into even small pieces. This will ensure they cook at the same time. Steam the potato pieces over high heat for 15-20 minutes, or until they're soft and can be easily pierced with chopsticks. Once the potatoes are done, take them out of the steamer and mash them until smooth using a spoon or rolling pin. Stir in 1/4 tsp salt and 1/2 tsp crushed black pepper. Set the mashed potatoes aside.

Prepare the Cucumber: Wash the cucumber and use a vegetable peeler to slice it into long, even strips. Try to keep the slices intact and consistent in width. Once sliced, roll up each cucumber strip and set them aside.

Prepare the Tuna: In a bowl, add 50g of cooked corn kernels. Open the tuna can and drain out most of the olive oil. You can place the tuna in a sieve to let the excess oil drip out. Once drained, add the tuna to the bowl with the corn. Add 1/2 tsp crushed black pepper, 1/4 tsp salt, and 1 tbsp mayonnaise. Mix well until the tuna absorbs all the flavors.

Assemble the Sushi: Form the potato mixture into small balls. Carefully place each ball inside a cucumber roll and press them down to flatten. Top with the tuna salad mixture and sprinkle with chopped parsley for a little extra flavor and color.