Heat a large pot of water to boiling. Make sure it is heavily salted.
While you wait for your water to boil, do your Mise en place: mince your garlic. Cut and juice your lemon. Finely grate 1 1/2 cups fresh parmesean cheese.
Once your water is boiling, add your spaghetti and cook until just al dente (usually 6-7 minutes). Reserve 1 cup of the pasta water for the sauce and then drain your pasta when done.
(As your pasta cooks) - Cook your pancetta in a large pan over medium high heat for about 7 minutes until crispy but not too dark.
Lower the heat to medium, add the olive oil, followed by the garlic, crushed red pepper flakes and pepper, and let cook until fragrant about 1 minute.
Add the lemon juice to the pan, followed by the drained pasta and toss to coat in the sauce. Then add the grated parmesean followed by the reserved pasta water, just a couple tablespoons at a time to help keep the cheese silky.
Add the arugula to the pan, toss with the pasta and let it wilt (about 1 more minute). Sprinkle with a little salt and if you like pepper or spice, add a bit more pepper or red pepper flakes to taste. Serve with grated parm on top.