While the spaghetti cooks in salted boiling water, prepare the sauce. Heat up some olive oil in a large saucepan. Add the garlic and chili pepper, to taste. When the garlic is golden, add the anchovies, olives, capers, and walnuts.
Let the mixture cook for about 1 minute before pouring the crushed plum tomatoes into the pan. Cook for approximately 10 minutes on medium heat.
About a minute before the al dente stage, drain the spaghetti and add it to the saucepan, allowing it to finish cooking in the sauce. Sprinkle the spaghetti with freshly chopped parsley and transfer to a warm plate. Serve immediately.
*If you like a spicy sauce, add the seeds along with the pepper. If not the pepper is optional.