Fry the onion, garlic and chilli until the onions are translucent.
Add mustard seeds, turmeric and garam masala and stir fry for 2-3 minutes.
Add the chopped tomatoes and keep cooking, stirring regularly, until tomatoes start to break up.
Pour beaten eggs into the pan, season with salt and cook, stirring constantly, until they are done.
You can serve this garnished with fresh, finely chopped coriander leaves.
Note: You can use less garlic than the recipe indicates if you don't like it that much, or even cut it out. I don't always have chillies on hand, so I leave them out - all this means is that the eggs will be slightly less spicy, but will still taste really nice.