Bring 4-5 l salt water (1 teaspoon salt per litre) to the boil.
Roast the walnuts in a pan for about 5 minutes while stirring. Wash parsley and shake dry, chop the leaves coarsely. Peel garlic and grate cheese coarsely.
Coarsely puree nuts, parsley, cheese, garlic and oil. Season to taste with salt and pepper.
Meanwhile cook the noodles in boiling salted water according to the instructions on the packet. Drain, collecting approx. 50 ml of pasta water. Mix linguine, pesto and pasta water.