Combine the shoyu, garlic, chilli, sesame oil and lime juice together. Finely slice the mushrooms and add the shallots. Pour the dressing over the mushrooms and leave to leave to marinate in the fridge for a few hours.
Wash and trim the spinach before lightly steaming it for 2 minutes.
Squeeze any extra moisture from the spinach. Set aside to cool. Serve the mushrooms with the spinach and top with sesame seeds.
Note: an easy way to squeeze excess moisture from spinach is to round it in a sushi mat, available from Asian grocers.