Clean the onion; chop it and put it in a heavy-bottomed frying pan with 2 spoonfuls of olive oil. Put the lid on the pan and cook over a very low heat for a couple of minutes. Remove the lid, pour in 2-3 spoonfuls of water and continue cooking, without putting the lid back on, until the onion is well cooked. In the meanwhile, wash the zucchini and pat them dry, then cut off the ends and dice them. Tip them into the frying pan with the onion, stir and cook over a lively heat for a couple of minutes. Now lower the heat, add 2 spoonfuls of warm water, season with salt and pepper and finish cooking. Transfer the zucchini into a tall, narrow container and blend with an immersion blender; taste the resulting cream and, if necessary, add salt. Skin the sausages and break them into pieces by hand. In the same frying pan in which you cooked the zucchini, sauté the clove of garlic with 4 spoonfuls of oil; when it has browned, remove it. Immediately tip in the pieces of sausage and sauté them, “crumbling” them up with the tip of a wooden spoon. Turn up the heat, pour in the red wine and when it has evaporated completely, turn the heat down again and cook for another 10 minutes. Cook the pappardelle in plenty of boiling, salted water, strain when “al dente” and toss them in the frying pan with the sausage; add the zucchini cream and mix the pasta and sauce together well. Sprinkle with the grated pecorino cheese and the coarsely chopped walnuts... and take your pappardelle straight to the table, nice and hot!