Remove the stem from the tomato and dice into 1cm cubes. Trim the root of the shimeji mushrooms and separate into small clusters.

Season the salmon with salt and pepper, then coat with all-purpose flour.

Heat butter in a frying pan over medium heat and cook the salmon until both sides are browned and cooked through. Remove, then flake the salmon while discarding the skin and bones.

Wipe the frying pan clean with a paper towel. Heat olive oil, add shimeji mushrooms, and sauté over medium heat until softened. Add tomato, grated garlic, salt, and water, then mix and bring to a boil.

Break the spaghetti in half and add to the pan. Cover and cook according to the package instructions, stirring occasionally. Return the flaked salmon to the pan and mix briefly.