Tip the rice into a bowl, cover with cold water and whisk for 1-2 mins till the water goes cloudy. Drain, rinse and tip into a small pan. Add 150ml boiling water and a pinch of salt. Pop on a lid, bring to the boil then turn the heat down very low. Gently simmer for 25 mins till all the water is absorbed, then take off the heat and leave to steam in the pan, lid on. The rice will stay warm in the pan.
While the rice cooks, peel and finely chop the onion. Warm a large pan over a low heat for 2 mins, then add the onion with ½ tbsp oil and a pinch of salt and pepper. Pop a lid on the pan and gently cook for 8 mins, stirring now and then, till the onion is soft and glossy looking.
While the onion sweats, roughly chop the tomatoes. Peel and chop the sweet potatoes into chunks around 1cm across. Peel and grate or crush the garlic clove.
Stir the garlic and tomatoes into the onions. Add 1 tbsp Bombay spice mix. Give it all a good stir and cook for 1 min till the pan smells aromatic.
Stir in the sweet potatoes. Drain the borlotti beans, rinse and add them too. Crumble in the stock cube and pour in 500ml boiling water. Put the lid back on the pan, turn up the heat and bring to the boil. Once the pan is boiling, turn the heat down and simmer for 15 mins, till the sweet potatoes are tender when pressed with a fork.
While the masala simmers, slice any thick cores out of the spring green leaves. Finely shred the leaves into thin ribbons.
Stir the spring greens into the masala. Simmer, without the lid on, for 5 mins till the spring greens are bright green and tender.
Taste the masala and add more salt or pepper if you think it needs it. Fluff the rice with a fork and spoon into 2 warm bowls. Ladle the masala over the top and serve straight away