First prepare your onion, tomato and green chillis by rinsing and slicing the onion, dicing the tomato and roughly chopping the green chillis. Also chop your fresh Coriander.
In a bowl add the eggs then the cumin powder, salt and pepper and mix the whole content. Continue to add the onion, tomato and chilli pieces and mix again.
Heat up a non stick frying pan, add 1 Tablespoon of butter first and add half of the liquid omelette mixture into the pan.
Cook on one side until golden brown, flip and cook the other side the same way. Do the same again with the remaining 1 Tablespoon butter and the rest of the omelette mixture.
Place the omelette into your cut open bread roll and add ketchup or a chili sauce in it.