Cut the top 2cm and flatten the bottom of the onions. Peel and hollow them out to create bowls. Dust with flour. Chop 1/4 of the hollowed onion finely and cut the rest into bite-sized pieces. Cut processed cheese into 1cm sticks. Separate shimeji mushrooms.

In a bowl, mix the meat mixture ingredients and finely chopped onion until sticky. Stuff the hollowed onions 70-80% full, insert processed cheese, and top with more meat mixture.

Heat olive oil in a pan and place the stuffed onions. Add the remaining onion pieces and shimeji mushrooms. Cook over medium heat for 2-3 minutes until browned.

Add the sauce ingredients and simmer covered over medium-low heat for 15 minutes. Remove the lid and simmer for another 10 minutes.