Trim any tough ends off the cavolo nero and finely shred the leaves. Slide into a bowl and set aside. Peel the garlic clove and crush or finely chop it. Peel and finely grate the ginger. Halve the chilli, scraping out any membrane or seeds for less heat. Finely chop the chilli.
Pour 1 tbsp oil into a pan and bring to a medium heat. Slide in the garlic and chilli along with a pinch of salt and pepper. Fry for 1 min, stirring frequently, till slightly golden.
Crumble the stock cube into the pan and pour over 800ml boiling water. Tip in the brown rice and stir well to combine. Bring to the boil, then partly cover with a lid and simmer for 20 mins.
After 20 mins, stir the cavolo nero and ginger into the soup. Cook for a further 5 mins, till the leaves have wilted and the rice is tender.
Grate the lime zest into the soup and squeeze in half of the juice. Have a taste and add a little more salt if needed. Ladle into bowls and serve.