Heat 1 tbsp oil in a large high sided frying pan, or a large casserole pan. Add the onion and cook over a medium heat for 4 - 5 mins until softened. Add the garlic, cook for a minute, then stir in the pasta, followed but a ladleful of stock. Cook, stirring until the stock is absorbed, then repeat until you have about 200ml of stock left.
Add the asparagus to the pan along with the remaining stock, cover and leave to bubble for 2 minutes. The pasta and asparagus should now be just tender. Stir in the crème fraiche and parmesan, season and leave with the lid on while you cook the fish.
Heat a large frying pan with the remaining oil until hot. Season the plain flour and then coat the fish with it. Cook the trout for 1 to 1 and a half minutes on each side until lightly golden. You may have to do this in 2 batches. Stir the basil into the orzo, divide between plates and top each with a piece of trout and a few basil leaves. Serve with extra parmesan if liked.