Heat the oil in a large, non-stick frying pan over a medium heat. Add the vegetables, in batches if necessary, and fry for 4-5 minutes, stirring regularly, until lightly browned all over. Season with salt and pepper.
Transfer the vegetables to the slow-cooker, sprinkle over the flour and stir well.
Add the chopped tomatoes, tomato purée and chili flakes then stir again. Pourover the stock and stir. Cover and cook on high for 4 hours.
After the hotpot has been cooking for 3½ hours, make the dumplings. Put the gluten free flour in a large mixing bowl and season with salt and pepper.
Mix the gluten free flour with the suet then stir in enough cold water to bring the mixture together as a soft, squidy dough. Divide into 12 equally sized pieces and roll each into a ball.
Remove the lid from the slow-cooker, stir in the spinach until wilted, then arrange the dumplings gently on top.
Replace the lid and continue to cook on high for a further 25-30 minutes, or until the dumplings are puffed-up and fluffy. Spoon the hotpot onto serving plates with the dumplings on top.