Cut the onion in half; mince one half and slice the other thinly. Trim the shimeji mushrooms and separate them into small clusters.

Place the minced onion in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 1 minute. Drain and let cool.

In a bowl, mix ground meat, microwaved onion, and ☆ ingredients until sticky. Divide into 4 portions and shape into oval patties.

Heat salad oil in a frying pan over medium heat. Add patties and cook until browned. Flip and cook for another 3 minutes. Add sliced onion, shimeji mushrooms, and ★ ingredients. Bring to a boil, cover, and simmer on low heat for 10 minutes, occasionally spooning sauce over the patties.

Sprinkle pizza cheese over the patties, cover, and steam for 3 minutes until the cheese melts.