Heat the oil in a large, heavy-based frying pan or wok, add the onion and cook over a medium-high heat, stirring frequently, for 3–4 minutes until beginning to soften. Add the cauliflower florets, the garam masala and the ground coriander and cook for 5 minutes, stirring almost constantly to prevent the cauliflower from catching, then add the 4 tablespoons cold water and cook for a further 2 minutes, stirring almost constantly.
Stir the chard leaves, cumin seeds and garlic into the pan and cook, stirring, for a further 2 minutes. Add the chickpeas along with the tahini, lemon juice and 150 ml (¼ pint) measurement water and season with salt and pepper. Toss the vegetables in the sauce, then reduce the heat, cover and simmer for 2 minutes. Season generously with salt and pepper.
Toss again before serving in warmed serving bowls with naan bread.