01 - Bring a large pot of salted water to a boil. Add the pasta and cook according to package instructions until al dente.
02 - About 3 minutes before the pasta is done, add the broccoli florets to the pot. Cook until both pasta and broccoli are tender.
03 - Reserve 1/2 cup of pasta cooking water, then drain the pasta and broccoli.
04 - In a large skillet, heat the olive oil over medium heat. Add the garlic (and red pepper flakes, if using) and sauté for 1 minute until fragrant.
05 - Add the drained pasta and broccoli to the skillet. Toss to combine, adding reserved pasta water as needed to create a light sauce.
06 - Stir in lemon zest, lemon juice, and Parmesan cheese. Season with salt and pepper to taste.
07 - Remove from heat, sprinkle with parsley, and serve with extra Parmesan if desired.