For the dressing mix vinegar, sugar, salt and sesame oil in a small saucepan and stir over a low heat until hot and sugar has dissolved. Cool and set aside until ready to use.
For the wasabi avocado, mash all ingredients roughly with a fork, set aside.
Place the rice and water in a saucepan and bring to the boil uncovered. Cover and reduce heat, then simmer gently for 20 minutes, or until tender. Turn off heat and stand for 10-15 minutes. Spoon over sushi dressing and fold gently with a large spoon to combine.
Heat oil in a frying pan. Add the mushrooms, salt and pepper and cook over a medium heat until cooked (about 5 minutes). Remove from the heat and set aside.
Add more oil to the pan and sear salmon in batches, cooking for 4 minutes each side over a medium-high heat. Rest for 10 minutes then flake with a fork.
Divide rice among 4 bowls. Top with salmon, wasabi avocado, mushrooms, mayonnaise, ginger, cucumber, radishes, a drizzle of soy sauce, sesame seeds and microgreens.