Heat the oil in the flameproof bowl of a 5L (20 cup) slow cooker or a large, deep frying pan over medium heat. Add the onion and cook, stirring occasionally, for 3 minutes, until softened. Add the mince and cook, breaking up the mince with a wooden spoon, for 3-4 minutes or until golden brown.
Push mince to the side. Add the extra oil. Add garlic, chilli, cumin and coriander. Cook, stirring, for 30 seconds. Combine with mince mixture. Transfer bowl to slow cooker.
Add pumpkin, capsicum, diced tomato, cherry tomatoes, corn and stock. Stir to combine. Cover. Cook on High for 3 hours.
Combine flour, polenta and salt in a large bowl. Add the butter and use your fingertips to rub butter into the flour mixture until mixture resembles fine crumbs. Stir in the cheese. Add the milk and stir until combined. Set aside for 5 minutes to thicken slightly.
Divide the mixture into 12 rough balls on a baking tray.
Place the dumplings into the stew. Fold a clean tea towel in half and place over the slow cooker. Cover. Cook for 1 hour or until the dumplings are cooked through. Sprinkle with coriander to serve.
