Stir the onion, chilli and sweetcorn kernels into the beaten eggs in a bowl. Season well with salt and pepper.
Melt the butter in a large saucepan until foaming. Add the egg mixture and cook over a medium heat, stirring constantly, until the eggs are softly scrambled. Immediately remove the pan from the heat and stir in the crumbled Manchego and coriander.
Serve immediately on the warmed tortillas scattered with green chilli slices, fresh coriander and chives, plus shavings of Manchego and the sweet chilli sauce.