Heat the oil in a pan, put in the cumin seeds and, when they splutter after a few seconds, add half the diced onion and cook until translucent.
Add the ginger and green chillies and brown lightly, then toss in half the diced tomatoes and stir-fry for 2 minutes.
Stir in the turmeric and red chilli powders, add the okra and cook for 2 to 3 minutes. Add the remaining onion and tomato and cook for a further 2 minutes.
Add the lemon juice, chaat masala and chopped coriander and serve hot with more fresh coriander and, if you like, cherry tomatoes, to garnish.
Tip: The flavour of okra or ladies fingers is best brought out by adding them last to a subtly spiced tomato mixture.