Peel the potatoes and slice them into thin slices about 5mm thick. Soak in water for 5 minutes and drain.

Place the potatoes in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 5–6 minutes.

Slice the onion thinly and drain the tuna can.

Heat a frying pan and add mayonnaise and sliced onion. Sauté until the onion becomes tender.

Add the potatoes, mixed beans, and tuna to the pan. Stir until the mayonnaise coats everything evenly.