Bring a large pot of salted water to a boil.
Cook rigatoni until al dente according to package instructions.
Reserve ½ cup pasta water, then drain.
Heat olive oil in a wide skillet over medium heat.
Add zucchini and cook for 4–5 minutes, stirring occasionally, until tender with lightly golden edges.
Season with salt and pepper.
Add garlic and chili flakes to the skillet and cook for 30 seconds until fragrant.
Lower heat and stir in lemon zest and lemon juice.
Add cooked rigatoni to the skillet along with reserved pasta water.
Toss gently until pasta is coated and glossy.
Remove from heat and stir in parmesan cheese (and butter or ricotta if using) until melted and creamy.
Taste and adjust seasoning with salt, pepper, or extra lemon juice.
Garnish with fresh herbs, toasted pinenuts and extra parmesan.
Serve immediately with a side salad, garlic bread, or roasted vegetables.
