Season the fresh salmon well with salt and pepper, and sprinkle with white wine (or sake). Let sit for about 10 minutes.
Prepare three 30cm sheets of aluminum foil, and spread vegetable oil (not listed) over the center of each. Divide the sliced onions into 3 equal portions, and place on top.
Separate the shimeji mushrooms, thinly slice the shiitake mushrooms and bell pepper, and cut the cherry tomatoes in half.
Place the salmon in top of the onions in the aluminum foil. Add the ingredients from step 3 on top, and add butter, salt, and pepper.
Bake in an oven preheated to 480F/250C for 12 minutes, and they are done.
Story Behind this Recipe
My mom used to make these in a pan, but I can prepare side dishes while these are steaming in the oven, so I changed the recipe like this...
When closing the aluminum foil in step 4, if you fold 1 cm of each end 2-3 time and again in the center, then the steam will not escape. When eating, I think adding a bit of soy sauce or ponzu sauce, if you prefer, is delicious. When opening the aluminum foil, it is really hot, so be careful not to burn yourself.