Bring a large pot of well-salted water to a boil over high heat.
Meanwhile, heat the oil and red pepper flakes in a 12-inch skillet over medium-low heat, stirring occasionally with a wooden spatula, until the pepper flakes are sizzling, about 5 minutes. Add the anchovies, if using, and mash them with the spatula until they begin to dissolve. Raise the heat to medium, add the breadcrumbs, and cook, stirring often, until the crumbs are deep golden, about 3 minutes. Add the garlic and cook, stirring, until the breadcrumbs are crisp and brown, about 1 minute. Remove from the heat, stir in the parsley, and season with salt to taste (if using anchovies, you may not need extra salt).
Cook the pasta in the boiling water according to package directions until al dente. Reserve 1/2 cup of the cooking water and drain the pasta. Immediately return the pasta to the pot over medium-low heat, add half the breadcrumb mixture and toss to combine. If necessary, add some of the reserved cooking water to moisten. Season to taste with salt. Serve sprinkled with the remaining breadcrumbs.