Tip the rice into a large bowl and cover with cold water. Whisk for 1-2 mins till the water goes cloudy (this is the starch). Drain and rinse. Tip the rice into a small pan. Add 300ml boiling water. Cover. Bring to the boil. Turn the heat right down. Simmer for 25 mins till all the water is absorbed.
While the rice cooks, finely slice half the red cabbage (see our tip for what to do with the rest). Finely grate the zest from the lime and set aside. Juice the lime into a large bowl. Stir in 1 tbsp sugar and 1 tsp sea salt. Add the shredded red cabbage. Stir to coat in the lime marinade. Set aside.
Chop the tomatoes into small dice. Peel and finely chop the onion. Peel and grate or crush the garlic. Finely chop the coriander stalks (keep the leaves for later). Drain and rinse the beans.
Warm a pan for 1 min. Tip in the sunflower seeds. Toast in the pan, shaking it a few times, for 2-3 mins till golden. Tip into a bowl and set aside. Add ½ tbsp oil and the onion to the pan. Season with salt and pepper. Cook and stir for 5 mins till the onion is glossy
Stir in the garlic, lime zest and coriander stalks. Add 1 tsp of the cumin and a pinch of cayenne. Stir in the beans and tomatoes. Cook over a low heat for 15 mins, stirring now and then, to warm the beans through and break the tomatoes down. Cover and set aside to keep warm.
The rice should have absorbed all the water by now. Take off the heat and set aside, lid on, for 5 mins to finish cooking the rice. Halve the avocado and discard the stone. Scoop out and dice the flesh.
Divide the rice between 2 warm bowls. Top with a tangle of the red cabbage, the warm black beans, sunflower seeds and avocado. Add 1 tbsp soured cream and a few coriander leaves to each bowl to serve.