Cook the pasta according to package instructions. Reserve 1 cup of pasta water, then drain and put the pasta back in the pot.
Mix the pesto, ricotta, and lemon zest together in a food processor or whisk together by hand. Add the pesto ricotta lemon mixture into the pot along with the reserved pasta water and stir vigorously until fully combined and all the noodles are coated.
Plate, and add any additional pesto, red pepper flakes, or a drizzle of good olive oil. Enjoy!