Read the recipe ahead of time. Take a few minutes to get everything measured, chopped & prepped. Roughly chop the garlic & parsley (if using), measure the cheeses, & gather all remaining ingredients. Set aside, within an arm's reach of the stove for easy, streamlined cooking.
Bring a large pot of generously salted water to a boil. Add the bucatini (or pasta of choice) & cook, stirring occasionally to prevent sticking, to al dente according to package directions. Important: before draining, carefully dip a liquid measuring cup into the pot, reserving about 1 cup of starchy pasta water, and set aside. Carefully drain the pasta - do not rinse!
Meanwhile, as the pasta boils, render the pancetta. Add diced pancetta to a large skillet over medium heat. Cook, stirring occasionally, until the fat renders & the pancetta becomes golden & crispy, about 5 minutes. Add in the chopped garlic & crushed red pepper flakes, if using. Cook, stirring constantly to prevent burning, for 1 minute more, until the garlic is slightly softened & very fragrant. Set aside.
Meanwhile, as the pasta cooks & pancetta renders, prep the carbonara sauce mixture. Add egg yolks, pecorino & parmesan to a large mixing bowl. Generously season with freshly cracked black pepper, as desired. Whisk to combine. The mixture will be thick. Set aside.
Add the pasta to a large skillet with the pancetta. Pour the sauce mixture over top. Working quickly, stir & toss. The mixture will be thick. While tossing constantly, slowly stream in a few tablespoons of the pasta water. Return skillet to medium low heat. Continue to toss, adding water little by little, or until warmed through, glossy & well-coated. Finish by tossing in the lemon zest, arugula & chopped parsley, if using.