Place all the ingredients up to and including the tomato in a food processor and blitz until smooth.
Tip the paste into a saucepan, add the oil and fry over a medium heat, stirring from time to time, for 3–4 minutes.
Pour in the coconut milk and add the frozen spinach. Simmer for 3–4 minutes to allow the flavors to mingle and the spinach to defrost.
Finally, add the defrosted prawns and cook for no more than 2 minutes, until they have just turned pink.
Stir through the lemon juice, if using, and serve.
