Thinly slice the mushrooms.
Heat a spoonful of oil in a frying pan and gently sauté the mushrooms for 5 minutes, then add the soy sauce and miso paste. Put the lid on and cook for a further 5-8 minutes, until tender.
Meanwhile, chop the spring onions and drain the lentils.
When the mushroom is tender, add the spring onion and lentils. Stir until warmed through.
Just before serving, add the chopped coriander and a dash of rice vinegar, then season with ground pepper (and a pinch of chilli flakes, if you like).
Serve warm.