Finely chop the onion and garlic.
Slice the mushrooms into bite-sized pieces.
Heat olive oil in a pan and sauté the garlic and onion.
Add the mushrooms and continue to sauté.
Pour in the tomato sauce and bring to a simmer.
Season with salt and pepper.
Cook the spaghetti noodles, then mix them with the sauce.
Serve in a bowl to finish.