Preheat your oven to 100C. Meanwhile rub your steak in the miso paste.
When the oven is ready, pop the steak on a tray and put it in. It will go in there for 15 – 20 mins, until the internal temperature is 45C (for rare), 55C (for well done). The steak will be finished in the pan and will cook further.
While the steak cooks, prep the veg. Chop the asparagus into 3cm lengths, the flat mushroom into long strips and dice the pepper into 1cm pieces. Get a pan on a high heat, add a splash of oil, a pinch of sugar and add the pepper.
After a couple of minutes stir frying, add the mushroom and asparagus. Cook for a further 3 – 4 minutes until everything is al dente, then add the rice. Move everything around until the rice is completely cooked, add the teriyaki and stir well. Taste for seasoning. Serve the rice on to plates and return the pan to a high heat.
Cook the steak for 30 seconds on each side until browned, making sure you cook the fat side as well. Move to a board (no need to rest) slice into finger-width strips and top your rice with the steak.