Bring a large pot of salted water to a boil. Add the spaghetti and cook until al dente.
Heat a large frying pan/skillet over medium-high heat then add the oil and garlic.
Add the chilli flakes and toast until the garlic starts to turn golden.
Add the shrimp and cook until pale pink and opaque throughout. Season with salt and pepper and add lemon juice. Add a few tablespoons of the pasta's cooking water and remove from the heat.
Once the pasta is cooked, carefully transfer the cooked spaghetti to the pan with the shrimp with a pair of tongs. Add a few tablespoons of the pasta cooking water and toss to emulsify.
Add the Parmesan and parsley and continue tossing until the pasta is well coated. At this point, you can add more water if you think the pasta needs a little extra sauciness. Taste and season to taste if necessary then serve with extra Parmesan.