In a large saucepan of salted boiling water cook pasta according to packet instructions. Reserve ½ cup of pasta water, then drain.
In a large frying pan heat the oils over medium heat. Add the garlic and cook for 30 seconds until fragrant. Add the prawns and cook for 2–3 minutes until pink and just cooked through.
Stir in the chilli oil, lemon zest, juice, sugar and soy sauce. Toss well.
Add the drained linguine, baby spinach and a splash of reserved pasta water. Toss over low heat for 1–2 minutes.
Serve immediately with a scattering of spring onion.