Cut off the stems of the shiitake mushrooms and separate the caps and stems. Dice the stems and dust the inner side of the caps with flour. Mince the onion and microwave it for 1 minute at 600W, then drain excess moisture.

Mix all the ingredients for garlic breadcrumbs in a bowl.

In another bowl, soak breadcrumbs in milk, then add the remaining meat filling ingredients and diced shiitake stems. Mix until sticky.

Divide the meat filling evenly and shape it onto the shiitake caps.

Heat the garlic breadcrumbs in a frying pan over medium-low heat until golden brown, then remove.

In the same pan, heat olive oil over medium heat. Place the stuffed mushrooms meat-side down and cook until browned. Flip, cover, and steam for 5 minutes.