Heat the oven to 200C with a fan / 180C without the fan / gas 6.
Cook the potatoes in a pan of salted boiling water for 3 minutes.
Add the asparagus and cook for a further 2 minutes.
Drain really well then run the asparagus under cold water and put aside.
Toss the potatoes with the olive oil and season generously (e.g. Italian herbs, rosmarin, salt, peppers).
Spread them over a large, non-stick baking tray or dish and roast for 15-20 minutes or until they’re starting to brown and almost tender.
Nestle in the trout and asparagus, and season again.
Roast for another 10-12 minutes or until the trout is just cooked.