While the linguine is cooking, prepare the mushrooms.
Heat the butter in a large skillet and add the mushrooms and saute' for a short time. Add a cover and a small amount of water and simmer for 5 minutes or until they are tender. Remove the cover and evaporate the liquid. Add the garlic and saute' until aromatic. Remove from the heat and season well to taste with salt and pepper.
When the linguine is tender, drain and return it to the pot and toss with the mushrooms, hazelnut oil and parsley until well combined. Garnish with hazelnuts and enjoy.