Cut the potatoes into bite-sized pieces and soak them in water for 5 minutes. Drain the water and place the potatoes in a microwave-safe container. Cover loosely with plastic wrap and microwave at 600W for 5 minutes. Drain any excess water.

Add salt to the hot potatoes and mash them with a fork until smooth. Mix in the mayonnaise and divide the mixture into 6 portions.

In a bowl, mix the tuna, green onions, salt, pepper, and mayonnaise to make the tuna filling.

Take one portion of the potato mixture and spread it on a piece of plastic wrap. Place one portion of the tuna filling in the center. Wrap and shape it into a ball. Repeat to make 6 balls.