Heat the oil in a frying pan, add the courgettes, garlic and spring onions and fry for 5 minutes until the courgettes are browned and just tender. Divide the mixture between 2 individual ovenproof dishes.
Beat together the eggs, cream and mustard in a jug, then season. Stir in half the cheese and pour the mixture over the courgettes.
Mix together the remaining cheese, the breadcrumbs and parsley in a bowl. Season and sprinkle over the egg mixture. Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 20 minutes until the tops are golden and the egg mixture has just set.