Heat oil in a 10-in/26-cm nonstick skillet and add eggs. When eggs start to set, swish them around so that the unset top rotates to the bottom. Sprinkle with chives, cheese and asparagus. Cook a minute longer, just until cheese starts to melt.
Meanwhile, warm and soften tortilla in a skillet (about one minute) or microwave (about 10 seconds), or wrap in foil and heat in a 300F (150C) oven for 10 minutes. Slide the omelette onto the tortilla and roll up. Cut in half on the diagonal for a sandwich or in slices for little appetizers.