Cook spinach in a large saucepan of boiling salted water until tender, 3 to 5 minutes. Drain. Rinse under cold water. Drain well.
Whisk eggs, egg whites, cumin and salt in a large bowl.
Coat a large non-stick frying pan with non-stick cooking spray. Heat over medium heat. Add egg mixture; stir until eggs start to thicken slightly, 2 to 3 minutes. Stir in spinach, ham and spring onion. Cook, stirring occasionally, until eggs are soft-scrambled, 2 to 3 minutes.
Spinach can be served raw or cooked. Stir-frying or steaming helps to retain its flavour and texture.