Tip the rice into a pan. Pour in 250ml boiling water. Cover. Bring to the boil. Turn the heat right down. Simmer for 6 mins till all the water has been absorbed. Take off the heat. Steam, lid on, for 4 mins till the rice is cooked.
Peel and grate the ginger. Trim and finely chop the spring onion. Heat 1 tbsp olive oil in a medium pan. Add the ginger and spring onion. Stir and fry for 1 min.
Add the chicken to the pan. Stir and fry for 5 mins till the chicken is beginning to brown. While the chicken cooks, peel the tough outer leaves from the lemon grass. Bash it a few times with a rolling pin to crush it.
Add the lemon grass to the pan with the coconut milk and miso, stirring to blend the miso in. Bring it up to a simmer. Cover and cook gently for 10 mins till the chicken is tender and cooked through. If the pan seems too dry, add a splash of water.
Meanwhile, cut the broccoli into florets. Put them in a steaming basket or colander. Pour enough boiling water into a pan to cover the base. Nestle the steamer basket in the pan. Steam for 3 mins till tender. Put to one side.
Wipe the mushrooms with kitchen paper. Slice any large ones. Heat 1 tbsp oil in a frying pan. Add the mushrooms. Fry for around 7 mins till juicy and a little golden.
Fluff the rice and stir in the broccoli and mushrooms. Taste and season the chicken if you think it needs it. Fish out the lemon grass. Serve the chicken with the rice.