Peel and finely chop the onion. Peel and crush or finely chop the garlic. Roughly chop the tomatoes. Halve the chilli, scraping out the seeds and white pith for less heat, and finely chop it. Set half the chilli aside for later. Separate the coriander leaves and stalks (keep the leaves for later in the recipe) and thinly chop the stalks.
Trim the stalk off the butternut squash and peel. Cut it in half and scoop out the seeds. Coarsely grate the flesh using a box grater. If you have a food processor, you can whizz the squash through the grating attachment to make this extra quick.
Pour 1 tbsp oil into a large pan and bring to a medium heat. Slide in the chopped onion, garlic, half the chopped chilli and half the coriander stalks. Sprinkle in 1 tbsp each smoked paprika and ground cumin, and a good pinch of salt and pepper. Fry for 5 mins, stirring occasionally.
Stir in the grated butternut squash, chopped tomatoes, 1 tbsp cocoa powder and 200ml boiling water. Cover with a lid and simmer for 25 mins, stirring from time to time, till the chilli is thick and the squash mince tender.
Meanwhile, heat your oven to 180°C/Fan 160°C/ Gas 5. Line a baking tray with greaseproof paper. Pour the polenta into a bowl. Coarsely grate the cheddar and add half to the polenta (keep the rest for later). Stir in the reserved coriander stalks and chilli. Sprinkle in a good pinch of salt and pepper and pour in 150ml cold water. Mix till well combined. Pat the dough into a 3-4cm high round and place on the lined baking tray. Slide into the oven and roast for 25 mins, till golden.
When the chilli is cooked, slide in the remaining half of the cheddar and stir till melted. Grate the lime zest and set aside. Squeeze the lime juice into the chilli and stir well. Taste the chilli and add more salt and pepper if needed.
Spoon the chilli into bowls and sprinkle with the reserved coriander leaves and lime zest. Serve with chunks of the cheesy cornbread on the side.