Heat the oven to 190°C/Fan 170°C/Gas 5. Pour 200ml boiling water into a large pan. Bring to a bubble then trickle in the polenta, stirring. Add 1 tsp cumin powder and plenty of seasoning. Cook for 5 mins till the polenta is thick. Using a couple of teaspoons, dollop little mounds onto a lined baking tray. It should make 10-12. Slide into the oven and bake for 15 mins till golden and crispy. Turn the oven off to keep them warm.
While the polenta bites are baking, peel and finely chop the onions. Peel and grate or crush the garlic. Halve the chilli, flicking out the seeds for less heat. Keep the seeds and you can add them to taste later. Crush the coriander seeds in a pestle and mortar till you have a coarse powder. Finely chop the coriander stalks, setting the leaves aside for later. Cut half the tomatoes in half and the rest into quarters.
Heat a large heavy based pan for a couple of mins. When warm, drizzle in 1 tbsp olive oil. Add the onions and fry for 5 mins till softened. Add in the garlic, chilli, coriander stalks and seeds and the tomatoes. Cook for 3-4 mins till the tomatoes have softened and the pan smells spicy.
Pour 400ml boiling water into the pan. Lower the heat and simmer for 5 mins. Drain and rinse the beans.
While the tomatoes are simmering, halve the avocado and scoop out the flesh. Pop it into a bowl and mash it with the back of a fork. Zest the lemon and set that aside. Squeeze a little of the juice into the avocado. Season generously. Taste and add more lemon or seasoning if it needs it.
After the tomatoes have simmered for 5 mins, Add the drained beans to the pan. Turn the heat up and cook for 10 mins. The liquid should have reduced by half. Remove a spoonful of the beans and liquid into a bowl. Crush with the back of a fork. Tip back into the pan. This will thicken the chilli.
Add the lemon zest and juice from half a lemon to the pan. Taste the white bean chilli. Add plenty of seasoning. Add a few chopped chilli seeds for more of a kick.
Ladle into warm bowls. Drop in a few polenta bites. Top with the smashed avocado and coriander leaves.