Place aburaage in a heatproof colander and pour boiling water over both sides to remove excess oil. Pat dry, cut in half along the shorter side, then slice into 1cm wide strips.

Trim the roots off the green onions and slice diagonally into 1cm pieces.

In a pot, combine all seasoning ingredients (sugar, mirin, soy sauce, dashi powder, water) and bring to a boil over medium heat. Add the aburaage, bring to a boil again, cover, and simmer on low heat for 5 minutes. Add the green onions and simmer for another minute.