1.Peel and thinly slice onion. Melt butter in large deep frying pan; cook onion, stirring, until softened.
2.Meanwhile, separate eggs. Beat egg whites in medium bowl with electric mixer until soft peaks form. Add egg yolks and peeled crushed garlic; beat until combined.
3.Fold half the rocket, half the chives and half the cheese into egg mixture. Pour mixture into pan; cook, uncovered, about 3 minutes or until omelette is almost set.
4.Sprinkle asparagus and ham over omelette; cook until omelette starts to come away from side of the pan.
5.Meanwhile, preheat grill (broiler).
6.Sprinkle remaining cheese over omelette; grill until browned lightly.
7.Toss remaining rocket and chives in oil and lemon juice. Serve omelette topped with rocket salad.
Gruyère is a hard-rind Swiss cheese with small holes and a nutty, slightly salty, flavour. It is a popular cheese for soufflés as it melts easily. Like a traditional soufflé, this soufflé omelette should be eaten straight away to prevent it sinking.Note