Preheat the oven to 180ºC/350ºF/Gas 4. Heat the oil in a large ovenproof casserole dish, add the onion, season with salt and pepper and cook for 10 minutes, until the onion is soft. Add the celery and carrots and cook for 4–5 minutes, then stir in the sweet potatoes and turn so everything is combined.
Add the tomato paste, thyme, tamari and peanut butter and stir again. Pour in the stock and bring it to the boil, put the lid on and put it in the oven for 1 hour. Keep an eye on it to check that it isn’t drying out at all – add a splash of boiling water if necessary. Add the jackfruit for the last 15 minutes, stirring it in so it is covered with the stock.
Meanwhile, prepare the dumplings. Put the flour, herbs, salt and pepper in a large bowl, and using your fingertips, rub the margarine into the flour until it resembles breadcrumbs. Slowly stir in the water until it comes together as a dough.
Pull out walnut-sized balls. You should be able to make about 12 dumplings, depending on how big they are.
Remove the pan from the oven and arrange the dumplings on top, pushing them slightly under the stock. Put the lid on and return the pan to the oven for another 15–20 minutes, until the dumplings are puffed up and golden. Remove from the oven and serve immediately.