Heat the cooking oil in a frying pan.

Add the onion slices to the hot oil and cook over medium heat, stirring often, until softened and just beginning to caramelize.

Turn up the heat to high, add the beef to the onion slices and stir to break up any clumps. Cook just until the meat is no longer pink.

Pour in the soy sauce, mirin, sake and dashi, and stir.

Turn down the heat to medium and cook, uncovered with occasional stirring, until the sauce has reduced to about two tablespoonfuls.

Scoop rice into four bowls, ladle the beef over the rice and top with shredded cheese.

Using a kitchen torch, heat the cheese until melted and toasted in spots.

Garnish your melty cheese beef rice bowl with sliced scallions, and serve immediately.