Coarsely chop the anchovies, slice the garlic and onion paper-thin and set aside.
While you bring the water for the pasta to a boil, heat the bread crumbs in a pan over a medium flame. Stir continuously till the bread crumbs become a nice tan colour. Remove the pan from the flame, pour half the oil into it and stir till all the bread crumbs are coated. Set aside.
When the water boils, salt it and add the spaghetti. While the spaghetti cooks, heat the remaining oil in a pan on a medium-high flame. Once hot, add the chopped anchovies and with a wooden spoon, mash them till they dissolve into the oil. Add the onion and garlic and let it cook till they just start to become golden, then add the chilli, reduce the heat and cook for another two minutes; set aside.
The pasta should be ready and al dente by now: drain it well and dress it with the anchovy-onion-garlic mixture. Add two thirds of the bread crumbs, the parsley and cheese (if using) and stir well. Serve with last sprinkle of the toasted bread crumbs and light drizzle of olive oil.