Cut the potatoes into bite-sized pieces and soak them in water. Shell the green peas.

Make a slit in the mentaiko and extract the contents.

Place the potatoes in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 4–5 minutes until soft. Mash lightly with a fork, leaving some texture, and let cool.

Boil water in a pot, add salt and green peas, and cook for 3–4 minutes. Drain and cool in cold water.

Combine the mashed potatoes, mentaiko, green peas, mayonnaise, powdered cheese, and pepper in a bowl and mix gently.