Wash your rice in cold water 3-5 times until the water runs clear. Drain in a sieve for at least 30 minutes.
Add your rice to a heavy-bottom pan with a tight fitting lid along with 220ml of water. Cover with the lid and bring to the boil. Turn the heat the low and cook for 10 minutes. Take of the heat and let steam for a further 10 minutes.
Meanwhile, prepare your mushrooms. Wipe the mushrooms clean and tear into strips. Sprinkle the cornflour over the mushrooms and toss to coat.
Heat the oil in a medium frying pan over a medium-high heat. Add your mushrooms and fry for 10 minutes, stirring often, until crispy and golden brown in places.
Stir together the soy sauce, mirin, and brown sugar. Add the sauce to the mushrooms and cook for 2 more minutes, stirring often. Remove the mushrooms from the pan and set aside.
Once your rice has finished steaming remove it from the pan and place it into a large, flat bottomed bowl.
Sprinkle your sushi seasoning over the rice and use a large spoon to fold it into your rice, fan the rice as you do so. Be careful not to stir the rice as this will make it mushy.
Cover with a damp tea towel and set aside until cooled.
Place a sheet of nori onto your rolling mat, shiny side down.
Wet your hands and top with ⅓ of your rice and spread over the nori, leaving 1cm clear at one end.
Add ⅓ each of the mushrooms, avocado and sliced vegetables to the rice. Arrange them in strips across the rice at the bottom of the nori sheet, at the opposite end to the 1cm you left clear of rice.
Dampen the end of the nori sheet and roll up from the bottom (where the veg is). Use the mat to shape a tight, round sushi roll.
Dampen a sharp knife and slice into 8 equal pieces, starting in the middle of the roll.
Repeat with the remaining ingredients.
Serve the rolls as soon as possible with the wasabi, ginger and soy sauce. You could also drizzle over sriracha mayo and crispy onions.
