Dice the new potatoes into 1cm cubes and soak in water to remove excess starch. Thinly slice the onion and soak in water for 5 minutes, then squeeze out the moisture.

Place the diced potatoes in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 3–4 minutes. Add the onion, corn, and ☆ seasonings (mayonnaise, yogurt, salt, and pepper) and mix well.

Spread ketchup evenly on the bread slices. Divide the potato mixture equally between the slices and sprinkle pizza cheese on top. Prepare two pieces in total. Toast in a toaster for about 3 minutes until the cheese melts.