Heat the oil in a pan and gently fry the onion and cumin seeds over a low heat, for 4-5 minutes. Increase the heat and add the ground coriander and mushrooms. Fry for 3-4 minutes. Stir in the chilli, tomato and butter. Once the butter has melted, add the whisked eggs and cook, stirring, over a moderate heat. Once the eggs are nearly cooked, remove from the heat and add the coriander and season with salt and pepper. Serve at once with pita bread or toast and lemon wedges, if desired.