Put the onion, garlic, ginger and chilli into a blender or food processor, and whizz until completely smooth. Heat the oil in a lidded, deep, 30cm frying pan and cook the onion purée and green pepper for 10 minutes with a pinch of seasoning until darkened in colour and the onion no longer smells raw. Stir in the cumin, turmeric and ground coriander, and cook for a minute before tipping in the tins of chopped tomatoes and 100ml of water, and simmering gently for 20 minutes or until the sauce has thickened. Stir through the spinach and chopped coriander, and cook for a minute until it wilts, then season. Make four indents in the sauce and crack the eggs into each. Put on the lid and simmer gently for 10-11 minutes or until the whites have set and the yolks are still runny.