Heat the oil in a medium saucepan.
Tip in the onion and ginger, then cook for a few mins until softened.
Stir in the curry paste, then cook for 1 min more.
Pour over the chopped tomatoes and coconut cream.
Bring to the boil, then leave to simmer for 5 mins, adding a little boiling water if the mixture gets too thick.
Tip in the prawns, then cook for 5-10 mins more, depending on how large they are.
Serve alongside some plain rice and sprinkle with a little chopped coriander, if you like.