Or for a thai green curry style sauce for fish:
Heat some oil in a wok until smoking hot. Add lots of chopped onion, spring onion, garlic and ginger and chilli if you want, quickly stir fry until onon os cooked. Add thinly sliced carrots, caugettes, peppers or any other stir-fry suitable veg you have, even if just peas.
then add the coconut milk and a mug of liquid that contains two teaspoons of cornflour mixed with two tablespoons of soy auce and filled up with cold water. Also add a stock cube. Heat all of this liquid in the wok until the cornflour has thickened and cooked, should take about five minutes. Add more salt, soy sauce to taste and a teaspoon of honey or brown sugar. Add the fish filets and cook on low heat until the fish is cooked, this shouldn;t take long. Either cut the fillets into chunks before adding or just flake them up once cooked.
Once cooked, add lots of chopped corainder and maybe a squeeze of loemn juice.
Serve with rice.