Trim the root of the shimeji mushrooms and separate them into bite-sized pieces. Slice the onion thinly, mince the garlic, and roughly chop the parsley.

Heat olive oil in a frying pan over low heat, add garlic, and sauté until fragrant. Add sliced onion and cook until softened, then add shimeji mushrooms and stir-fry briefly.

Boil water in a pot and cook spaghetti 1 minute less than the package instructions. Drain and add to the frying pan with the vegetables. Mix in soy sauce, butter, pepper, and consomme powder until well combined.