Add the pesto sauce into a large serving or mixing bowl and set aside.
Cook the pasta:
Bring a large pot of water to a boil. Once boiling, add the fusilli and boil according to the package directions. Once the pasta is ready, reserve 1 cup of pasta water.
Drain the pasta water and transfer the fusilli into the large bowl containing the pesto. The pot will be too hot and will dry the pasta.
Combine:
Pour half of the reserved pasta water into the bowl with the pesto and pasta. Use kitchen tongs to combine the sauce. Add more pasta water slowly until the pesto coats all of the noodles and you like the consistency of the sauce. I typically use between ¾ and 1 cup of water total.
Serve:
Serve the pesto fusilli in pasta bowls topped with Parmesan cheese and enjoy!