Put the oil in a wide pan and set over medium–high heat.
When hot, add the cumin seeds.
As soon as the seeds begin to sizzle, add the onion.
Stir and fry until the onion browns.
Add the ginger and garlic, stirring until the garlic starts to brown.
Add the mushrooms.
Stir and fry for 2 minutes.
Add the beans, coriander, cumin, turmeric, garam masala, chilli powder, salt, tomato and 120ml (4fl oz) water.
Bring to a boil.
Cover, lower the heat and simmer for 15 minutes.
Remove the cover, raise the heat and boil most of the liquid away, stirring gently as you do so.