Start by making the pangrattato. Cut the bread into small cubes and grind in a food processor until you get breadcrumbs with a good texture to them... nothing too fine. Heat a generous amount of oil in a large pan and add the garlic and thyme. Once the garlic gets golden, add the breadcrumbs and toast them in the oil until they are nicely browned. Discard the garlic and herbs, season with salt, stir in the parsley and transfer to a plate lined with paper towels. Once cool, transfer to a bowl.
Bring a large pot of copiously salted water to boil, and add the pasta.
Heat oil in a large pan over medium heat. Add garlic and cook until just light brown, then add the anchovies (watch out for the splatter). Cook until they fall a part.
Add the red pepper flakes, parsley and lemon juice and swirl the pan. Set aside until the pasta is ready.
Drain pasta 1 minute short of al dente. Add to pan with the sauce and arugula. You will need to splash a good bit of pasta cooking water into the pan to get the sauce adequately loose.
Toss over high heat for a minute until well mixed and arugula is wilting.
Pour into a serving bowl and sprinkle with the seasoned breadcrumbs. Serve with more of the breadcrumbs on the side.