Half-fill a large, non-stick saucepan with water and bring to the boil. Add the pasta to the boiling water, return to the boil and cook for 8 minutes, stirring occasionally. Add the broccoli to the pan and cook for 2 minutes more.
Drain the pasta and broccoli. Return to the pan and add the tomatoes, prawns, oil, chilli flakes and season well. Cook for 2–3 minutes, tossing with two wooden spoons until the spaghetti is evenly coated with the spices from the pan and the prawns and tomatoes are hot.
Squeeze over a little lemon juice, if using, and serve immediately.
