In an ovenproof 25 cm (10 inch) non-stick skillet, cook spinach over medium heat, stirring for about 2 minutes or until wilted. Add pepper, garlic and hot pepper flakes; stir to combine. Add oil and cook for 3 minutes or until softened.
In a bowl, whisk together eggs, water (or skim milk), and cheese. Pour into skillet and stir to combine with spinach. Lift edges with a rubber spatula and let eggs run to the bottom. Let cook, until edge starts to set.
Place skillet about 10 cm (4 inches) under broiler for about 3 minutes or until top is set and light golden. Use a digital food thermometer to check that the eggs have reached an internal temperature of 74°C (165°F).