Soak dried hijiki in a bowl of water according to package instructions. Drain well.

Wash new potatoes thoroughly without peeling. Cut into bite-sized pieces and soak in water briefly. Drain.

Place new potatoes in a pot with enough water to cover them. Heat over medium heat until boiling, then cover and simmer on low for 8–10 minutes. Add green peas, cover, and cook for another 2 minutes. Drain water and heat on medium, shaking the pot until potatoes turn white and dry. Let cool slightly.