Salt and pepper the salmon fillet. Place on a sheet of baking paper.
Put the garlic, onion, lemon and the sprig of rosemary on top. Halve the cherry tomatoes, cut the mushrooms into cubes or slices and spread everything around the fish. Sprinkle everything with the olive oil.
Seal the parchment paper and twist the ends like a candy. Steam in the oven for approx. 15 minutes at 180 ° C. A really great aroma emerges from the package when it is unpacked. All you need is baguette.