Bring a large pot of salted water to a boil and cook spaghetti until al dente, reserving some pasta water before draining

Heat olive oil in a large skillet over medium heat

Add garlic and sauté gently until fragrant but not browned

Sprinkle in red pepper flakes and stir for a few seconds

Add fresh spinach in batches, stirring until wilted and reduced in size

Pour in a small amount of reserved pasta water to create a light sauce

Add the cooked spaghetti directly into the skillet

Toss everything together until the pasta is well coated

Season with salt, pepper, and lemon juice if using

Sprinkle Parmesan cheese on top and serve immediately