Heat a tiny amount of oil in a non-stick omelette pan. Beat the egg whites with a fork and add the chives, salt and ground pepper. In a separate pan, toss asparagus in some oil until heated through, then season with salt and ground pepper. Set aside and keep warm. Pour the egg white into the oiled omelette pan and, with a fork, quickly draw the edges to the centre, so the omelette cooks evenly. When cooked but still creamy place the asparagus in the centre and leave on the heat for a second longer. With a fork fold the omelette towards the far lip of the pan, giving the pan a light tap to loosen the omelette. Slide out onto a warm plate.