Bring a large quantity of heavily salted water to a boil in a large pot over high heat. Once boiling, add the spaghetti and cook, stirring occasionally, according to package directions until al dente, about 8 minutes. Meanwhile, if using red pepper flakes, heat the oil add flakes, then saute in a small saute pan for 1-2 minutes to allow the oil to absorb the spiciness. Allow the red pepper oil to cool. In a large bowl or measuring cup, whisk together the olive oil, Parmesan cheese and lemon juice. Drain the pasta, reserving 1 cup of the cooking liquid. Place the drained pasta in a large, high sided saute pan over medium heat. Add the lemon sauce and toss the pasta to distribute the sauce. If the pasta is too tight, add the reserved pasta cooking liquid, 1/4 at a time, then continue tossing until sauce loosens up. Add chiffonade prosciutto and continue to toss to distribute. Correct seasoning with salt and pepper. Garnish with lemon zest and chopped basil, then serve immediately.