Crumble the stock cube into a heatproof jug and stir in 800ml boiling water. Stir to dissolve. Pour the stock into a medium pan. Set over a medium heat, cover and bring to the boil.
When the stock has started to boil, turn the heat down. Slowly pour the polenta into the stock, trickling in a little at a time, and whisking as it hits the pan to smoothly combine it. Once all the polenta has been added, put the lid back on. Turn the heat down very low. Cook for 25 mins, stirring a few times, till the polenta is thick and pulls away from the edge of the pan when you stir it. Be careful as the polenta will pop and splutter. Keep the heat low and a lid on the pan, carefully taking it off to give the polenta a quick stir now and then.
While the polenta simmers, add 2 tsp cumin seeds to a separate dry pan. Set over a medium heat and toast for 2 mins till the cumin seeds pop and smell toasty. Tip into a bowl and set aside.
Peel and finely chop the onion. Put the clean pan back on a medium heat for 2 mins. Add 1 tbsp oil, the onion and season with salt and pepper. Cook for 8 mins, stirring now and then, till the onion looks glossy and has softened.
While the onion cooks, peel and grate or crush the garlic. Drain the aduki beans and give them a good rinse. Stir the garlic into the onion. Add half the cumin seeds, 1 tsp smoked paprika and a pinch of cayenne (it’s spicy, so use as much or as little as you like). Cook and stir for 2 mins till the pan smells aromatic.
Tip the beans into the pan. Pour in 200ml boiling water. Pop on a lid, bring to the boil, then turn the heat down to medium-low. Simmer for 10 mins, stirring occasionally, till the aduki beans are soft.
While the beans simmer, quarter the tomatoes. Halve the avocado and scoop the stone out with a spoon. Scoop the flesh out of the skins. Dice the avocado. Pop in a bowl and squeeze in the juice from the lime. Gently mash with the back of a fork.
Taste the beans and add a pinch more salt or pepper if you think it needs either. Take the polenta off the heat, let it cool for 1-2 mins, then taste and season with salt and pepper.
Spoon the polenta into 2 warm bowls. Top with the beans, tomatoes and the smashed avocado. Scatter over the remaining toasted cumin seeds, a pinch of smoked paprika and serve.