Bring water to a boil in your pot with a large three-finger pinch of salt. Once it's boiling, add your pasta and cook until al-dente (usually about 1 - 2 minutes less than the instructions say, taste a noodle to test).
Reserve 1 cup of the pasta water, then drain it and set the pasta aside. Do not rinse the pasta.
To the same pot you just used to cook your pasta, add the ricotta cheese, lemon zest and juice, parmesan cheese, grated garlic, red pepper flakes, salt, and pepper. Mix until well combined.
Add your pasta back into the pot with the sauce along with ½ cup of reserved pasta water. Mix until well combined, adding more reserved pasta water as needed to thin it out to your liking.