Heat the oil in a large saucepan set over a low to medium heat. Add the onion, garlic, peppers and pumpkin and cook, stirring occasionally, for 10–12 minutes, or until tender.
Stir in the chilli powder or chipotle paste, along with the ground cumin, coriander and cinnamon. Cook for 1 minute, then add the oregano, tomato purée, tomatoes, black beans and vegetable stock. Increase the heat to bring to a boil, then reduce the heat to low and simmer gently for 30–40 minutes, or until the liquid reduces and thickens.
Season to taste with salt and pepper, and stir in the chopped coriander.
Serve the chilli in shallow bowls with rice (if liked), and lime wedges on the side for squeezing. Everyone can help themselves to the toppings.