Fill a large pot with water and add a generous pinch of salt. Bring the water to a rolling boil. Add your spaghetti and cook according to the package directions until it reaches “al dente” texture. Before you drain the pasta, scoop out about one cup of the starchy pasta water and set it aside. Drain the remaining water and keep the pasta in the colander.

Place the same pot back on the stove over medium heat. Pour in the olive oil. Once the oil is shimmering, add the minced garlic and the red pepper flakes. Sauté for about 1 to 2 minutes until the garlic is fragrant and golden, but be careful not to burn it. Burning the garlic will make the oil taste bitter.

Add the cooked pasta and the fresh baby spinach to the pot with the garlic oil. Pour in the lemon juice and half of the reserved pasta water. Use tongs to toss everything together vigorously. The heat from the pasta will wilt the spinach in about 60 seconds. Add the lemon zest and more pasta water if the noodles look too dry. Season with salt and pepper. Top with parmesan cheese if you are using it, and serve immediately.