In lightly salted water, cook spaghetti for 1 minute less than the box instructs.
Heat olive oil in a sauté pan over medium heat. Add garlic, pepper flakes and anchovies to the pan. Cook until the anchovies dissolve, stirring to help melt them. Remove from heat and squeeze the lemon juice into pan; swirl to combine.
With 30 seconds left on the pasta, add arugula to the pasta water and stir. Transfer all spaghetti and arugula to sauce pan. Turn heat to medium-low and toss, toss, toss!
Remove to a plate. Grate bottarga directly overtop. Enjoy!