Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Line a tray with baking paper. Bring 3-4 l salt water (1 teaspoon salt per litre) to the boil. Peel and finely chop the garlic and onion. Wash herbs, pluck off leaves and chop. Crumble bread, mix with oil and 1⁄3 each garlic and herbs. Spread on the baking tray and bake in the oven for about 10 minutes.
Cook the pasta in salted water according to the instructions on the packet. Clean and slice the mushrooms. Sauté mushrooms, onion and the rest of the garlic in hot butter. Add the rest of the herbs and about 100 ml of pasta water, bring to the boil and season with salt and pepper. Drain the pasta, put it back into the pot and mix in the mushrooms. Sprinkle with crumbs. If you like, sprinkle grated cheese on top.