Heat oven to 200C/fan 180C/gas 6. Cook the asparagus in a pan of boiling salted water for 1 min, drain, then run under the cold tap for a few secs. Drain again, toss in olive oil and spread out to a single layer in a large ovenproof roasting tin. Check the salmon for pin-bones, then arrange on top of the asparagus.
To make the crust, finely grate the zest of 1 lemon, then add this to the butter, breadcrumbs and pepper, and sprinkle liberally over the salmon. Cut the lemons into wedges. Nestle two-thirds of the wedges around the fish, then squeeze the juice from the remainder directly over the fish.
Roast fish for 12-15 mins or until it is just cooked through, it should be opaque and firm (see How to cook it, below left). Sprinkle with chives, then serve immediately with buttered new potatoes.