1. Bring a large pot of salted water to a boil and cook the spaghetti until al dente. Reserve 1/2 cup of pasta water, then drain.

2. While the pasta cooks, thinly slice the garlic and finely chop the parsley.

3. Heat the olive oil in a large skillet over medium-low heat.

4. Add the sliced garlic and cook gently until fragrant and lightly golden, about 2 to 3 minutes.

5. Stir in the red pepper flakes and cook for 30 seconds.

6. Add the drained spaghetti to the skillet and toss to coat in the garlic oil.

7. Pour in the reserved pasta water and toss until the sauce becomes glossy and lightly coats the pasta.

8. Add the parsley, salt, and black pepper, then toss again.

9. Serve immediately with parmesan cheese and lemon zest if using.