Cook the Pasta: Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the spaghetti and set aside.
Prepare the Garlic Butter: In a large skillet, melt the butter over medium heat. Add the minced garlic and red chili flakes, sautéing for about 1-2 minutes until the garlic is fragrant but not burnt.
Combine With Pasta: Add the drained spaghetti to the skillet with the garlic butter. If the mixture appears dry, slowly add some of the reserved pasta water until the desired consistency is reached.
Add Cheese and Seasonings: Stir in the grated Parmesan cheese, salt, black pepper, lemon zest, and lemon juice. Toss everything together until the cheese has melted and the pasta is evenly coated.
Finish and Serve: Remove from heat and fold in the chopped parsley for a fresh touch. Adjust seasonings if necessary.
Plate it Up: Serve the spaghetti in warmed bowls, with additional Parmesan cheese sprinkled on top and a drizzle of high-quality olive oil if desired.
Notes
Adjust the red chili flakes to taste for desired spiciness.