Bring a large pot of heavily salted water to a boil. Add the spaghetti or linguine and cook according to package directions until al dente.

Before draining, reserve about 1 cup of the starchy pasta water. Drain the pasta and set aside.

While the pasta cooks, heat the olive oil in a large skillet or non-stick pan over medium-high heat. Add the sliced zucchini and cook, stirring occasionally, for 5-7 minutes until tender-crisp and lightly browned. Do not overcrowd the pan; cook in batches if necessary.

Reduce heat to medium. Add the minced garlic and red pepper flakes (if using) to the skillet with the zucchini. Cook for 1-2 minutes until fragrant, being careful not to burn the garlic. Stir in the lemon zest.

Add the cooked and drained pasta to the skillet with the zucchini mixture. Pour in the fresh lemon juice and 1/2 cup of the reserved pasta cooking water. Toss everything together vigorously until the pasta is well coated and the sauce slightly emulsifies.

Remove the skillet from the heat. Stir in the 1/2 cup of grated Parmesan cheese. Continue to toss until the cheese has melted and created a creamy sauce. If the sauce seems too dry, add a splash more reserved pasta water until desired consistency is reached.

Season the pasta with salt and freshly ground black pepper to taste. Garnish with fresh chopped parsley or basil, and serve immediately with extra Parmesan cheese on the side.