Whisk the eggs in a bowl to combine before adding the milk, finely chopped spinach, parmesan, herbs and finely chopped chilli. Mix well.
Head a small pan over a medium heat and add a dash of olive oil and melt a small knob of butter. Add to this the egg mixture and swirl the pan so that the mixture covers it evenly. Leave to cook on one side for two minutes before carefully flipping. Cook for 10 seconds before folding in half and in half again. This will ensure the omelette isn't overcooked and still retains a custardy centre.
Serve on toasted sourdough or simply on its own drizzled with chilli oil.