Step 1 Place onion and 6 cups water into a medium saucepan and bring to the boil. Add salmon, cover and simmer gently for 5 minutes. Remove saucepan from heat and set aside for 5 minutes. Carefully remove salmon from liquid and set aside to cool. Flake salmon into chunks.
Step 2 Meanwhile, cook noodles in a large saucepan of boiling water following packet instructions, adding sugar snap peas and asparagus in last 2 minutes of cooking. Refresh under cold running water. Drain well.
Step 3 Place noodles, vegies and salmon into a large bowl. Whisk together soy, mirin and sesame oil. Add to salad and toss to combine. Season with pepper.