In a large pot of boiling water, cook the spaghetti to al dente according to package directions. Set aside 1 cup of pasta water, then drain the pasta.
In a large non-stick skillet cook the pancetta/bacon over medium heat until crispy, 5-7 minutes. Add in the olive oil, garlic, red pepper flakes and black pepper, cooking for around a minute.
Add in the lemon juice and drained pasta to the bacon mixture and stir to evenly mix. Next, sprinkle in the grated Parmigiano and slowly add in 1 tbsp at a time of the reserved pasta water. This is just to help the cheese mix into the pasta (I only use 1 tbsp total).
Add in the arugula and stir for 1 minute. Season with salt, pepper and red pepper flakes. Top with freshly grated Parm and enjoy!