Tip the rice into a bowl and cover with cold water. Set aside to soak.
Pop the porcini mushrooms in a heatproof jug and pour in 450ml boiling water. Stir to mix a few times, then set aside to soak too.
Peel and finely slice the onion. Trim, scrub and finely chop the carrot. Trim and finely dice the courgette.
Put a deep frying pan or wok over a medium heat and let it warm for 1 min, then add the onion, carrot and courgette with 1 tbsp oil. Season with a little salt and pepper. Fry for 5 mins, stirring now and then, till the veg start to pick up a little colour.
While the veg fry, thinly slice the shiitake mushrooms. Peel and crush or grate the garlic. Peel and grate the ginger. Drain the lentils and rinse under cold water.
Stir the shiitakes into the veg with the garlic, ginger and miso. Cook and stir for 2 mins, then tip in the lentils. Pour in the porcini with their stock. Pop a lid on the pan, turn the heat up and bring it to a simmer. Once it has started to bubble, turn the heat down and little and simmer for 8 mins.
While the lentils simmer, drain the rice and tip it into a small pan. Pour in 300ml boiling water and add a pinch of salt. Cover with a lid and bring to the boil, then turn the heat right down and very gently simmer for 8 mins till all the water has been absorbed. Take the rice off the hat and let it sit in the pan for 5 mins, with the lid on, to steam.
Finely slice the spinach leaves. Trim the roots and top 1cm off the spring onion, then finely slice it on the diagonal.
Stir the spinach into the lentils and simmer, without the lid on, for 2 mins to just wilt it. Taste the lentils and add a pinch more salt or pepper if you think they need it.
Fluff the rice up with a fork and spoon into 2 warm bowls. Spoon over the miso lentils and serve, garnished with the sliced spring onion.