Heat the oil in a frying pan and fry the onion and barley for 5 minutes. Transfer to a large casserole dish. Add 400ml water with the remaining ingredients except the coriander. Bring to the boil, cover and bake for 45 minutes, stirring half way through.
Stir in the coriander and season to taste.
Hint and tip: try adding diced chicken for a meaty option.