Set oven to warm. Pour 2 tsp (10 mL) oil into a medium frying pan over medium heat; add onion and sauté until softened, about 5 minutes. Add garlic, tomatoes, and asparagus; simmer about 5 minutes. Toss in basil; remove from heat.
Meanwhile, in a large bowl, whisk eggs with 1 tbsp (15 mL) cold water. In a large frying pan, heat 1 tsp (5 mL) oil over medium heat. Pour in half the beaten eggs. Lift edges gently inward as eggs set, allowing the uncooked portion to flow underneath.
When the top is set and the underside is browned, spoon half of the asparagus/tomato mixture onto one half, sprinkle with half the feta, then use a spatula to flip the omelette's other half overtop.
Transfer to an ovenproof dish and keep warm in oven. Repeat with remaining oil, eggs and filling. Place half an omelette on each of 4 plates. Garnish with olives.
Per serving: 214 calories, 14 g protein, 15 g total fat, 5 g saturated fat, 381 mg cholesterol, 6 g carbohydrates, 2 g fibre.