Cook the pasta in a large saucepan of salted boiling water according to the packet instructions until al dente.
Meanwhile, melt the butter with the oil in a large frying pan over a medium heat, add the garlic, spring onions and chillies and cook, stirring, for 2–3 minutes. Increase the heat to high, add the prawns and cook, stirring, for 3–4 minutes, or until they turn pink and are just cooked through. Stir in the lemon juice and coriander, then remove from the heat.
Drain the pasta thoroughly and add to the prawn mixture. Season well with salt and pepper and toss. Serve immediately, garnished with coriander leaves.