Snagged this from the Ken Hom bloke.
In a pan (if you love watery soup packed with flavour use a HUGE pan, if you want tRy a bit use small pan).
Add finely chopped lemon grass, peel of a lemon, juice of a lemon, 1 red chilli, 2 or 3 spring onions, coriander, 1lb fresh tomatoes. Fill up with veg stock, leave to simmer.
That's it.
If you want to make a meal of it, put rice noodles or very fine noodles on a bowl, ladle soup over the noodles and leave it for 3-4 minutes and eat.
Über simple!