Place the celery and carrots into a slow cooker. Heat the oil in a large non-stick frying pan, then fry the beef in two batches until golden-brown, transferring to the slow cooker when ready. Scatter with the ginger and chili.
Stir the sugar, gluten free soy, stock and sesame oil into the juices in the frying pan then bring to a simmer, stirring to dissolve the sugar.
Pour the hot liquid over the beef and vegetables, cover with the lid and cook on low for 7½ hours.
Scatter with the scallions (green end only), re-cover the slow cooker then cook for another 30 minutes.
Stir in the beansprouts, then drizzle with a little more sesame oil. Serve with steamed rice.