Heat the oven to 220C (200C fan)/gas 7. Put the squash and celeriac on a baking tray, drizzle over half the oil and season generously. Toss everything together with your hands, spread out and roast for 30-35 minutes, until the veg is tender, and crisp and golden around the edges.
Toast the dried chillies in a small, dry frying pan for a minute on both sides, then cover with boiling water and set aside. Meanwhile, pour the remaining oil into a large saucepan, add the onions and sweat over a medium heat for 10 minutes, until they begin to soften. Season generously, add the garlic and cook for another five to seven minutes.
Drain the chillies, chop them finely, add half to the onions, along with the spices and oregano. Fry for a minute, then add the beans, tomatoes, sugar and chocolate. Fill the tomato tin with hot water and add to the pan.
Bring to a boil, then simmer for 15 minutes until reduced. Stir in the roast vegetables and check the taste – if you want more spice, add the rest of the chillies. Simmer for another 15 minutes, until the sauce has thickened, check the seasoning, then sprinkle over the coriander and serve with guacamole, rice and soured cream.