Put a small saucepan on a medium heat, add the butter and when it has melted, add the quartered cherry tomatoes and the chopped red or green chilli, whichever you're using. Cook for 2-3 minutes, covered with a lid, until the tomatoes and the chillis are soft.
Crack the eggs into a bowl, add the milk, season with a good pinch of salt and some freshly ground black pepper, and beat together. Pour the egg-and-milk mixture into the tomato-and-chilli mixture, reduce the heat and cook for 2-3 minutes, stirring continuously, until the eggs are softly scrambled.
Stir in the finely chopped red onion and the roughly chopped fresh coriander and check the seasoning, adding more salt and freshly ground black pepper if necessary. Divide between plates and serve the eggs either on their own, or on top of warm tortillas or buttered toast.