Boil a saucepan of water and stir in the miso paste. Cook the basmati rice in this water according to the pack instructions.
Dip each mushroom into the beaten egg, then coat with breadcrumbs. Put them on an oven tray and spray with vegetable oil. Cook for 15 to 20 minutes until golden.
Meanwhile, heat a saucepan with a little oil and cook the carrot, celery and onion with a lid on until soft, about 5 minutes. Season and stir in curry powder. Add the flour and stir well. Slowly pour in the stock, whisking well. Cook for about 5 minutes until you have a thick and glossy curry sauce. Strain the sauce through a sieve or blitz it until smooth.
Serve with the miso rice and top with a breaded mushroom.