Fill a large pot with water, add salt, and bring it to a rolling boil. Cook the rigatoni according to package instructions, around 10-12 minutes, until al dente. Reserve a cup of pasta water before draining.

Heat olive oil in a large skillet over medium heat. Add minced garlic and sauté for about 1 minute until fragrant and lightly golden.

Add spinach or arugula to the skillet and sauté for about 2 minutes until wilted.

Lower heat and add ricotta, lemon zest, and lemon juice. Stir until smooth, adding reserved pasta water as needed for consistency.

Fold in the drained rigatoni and mix to coat. Add Parmesan and stir until melted.

Season with salt, pepper, and red pepper flakes if desired. Serve immediately garnished with lemon zest.