Preheat the oven to 220C/425F/Gas 7.
Place the asparagus into an ovenproof dish with half of the olive oil and season, to taste, with salt and freshly ground black pepper. Stir well, then place into the oven and roast for 8-10 minutes, or until just tender and lightly charred.
Meanwhile, bring a large pan of water to a rolling boil and add the vinegar. Swirl the water to make a whirlpool, then crack in the egg. Poach for 2-3 minutes, until just set.
Heat the remaining olive oil in a frying pan and add the garlic and prawns. Fry gently for 2-3 minutes until the prawns have turned pink and are cooked through. Season, to taste, with salt and freshly ground black pepper.
To serve, place the roasted asparagus onto a warmed plate and scatter the prawns over the top.
Remove the poached egg from the water and drain briefly on kitchen paper. Trim off any ragged edges.
Place the egg on top, season with freshly ground black pepper and sprinkle with chives.