Wilt the spinach in a non-stick frying pan over high heat, stirring frequently, or place spinach in a microwave-safe bowl, cover with vented plastic wrap and microwave on high for 1 to 2 minutes until just wilted. Press out the excess liquid and chop coarsely. Place the spinach in a small bowl. Stir in the cheese and spring onions.
Blend egg, egg whites, Tabasco and pepper briskly with a fork in a medium bowl. Heat oil in a 18- to 25-cm non-stick frying pan over medium-high heat until hot. Tilt the frying pan to swirl oil over surface. Pour in egg mixture. Immediately stir egg mixture with a heat-resistant rubber spatula or fork for a few seconds. Then use the spatula to push cooked portions at the edges towards the centre, tilting the frying pan to allow uncooked egg mixture to fill in areas around the edges. Sprinkle spinach mixture over the omelette. Continue to cook until almost set and the bottom is golden. The entire cooking process should take about 1 minute.
Use a spatula to fold one-third of the omelette over the filling. Tip the frying pan and, using the spatula as a guide, slide the omelette onto a plate so that it lands, folded in thirds, seam side down.
Mushroom omelette: Omit the spinach, goat cheese and spring onion. In Step 1, heat 1 teaspoon oil in a medium non-stick pan over medium-high heat. Add ½ cup sliced mushrooms. Cook, stirring often, until browned, 3 to 4 minutes. Stir in 1 tablespoon parsley and a pinch of black pepper. In Step 2, sprinkle the mushroom mixture over the omelette. * Broccoli and cheese omelette: Substitute 2 tablespoons chopped cooked broccoli and 2 tablespoons shredded Swiss or cheddar cheese for the spinach, goat cheese and spring onions in the filling.