Make the meatballs:
Mix all meatball ingredients together with your hands, ensuring they are well combined. Wet your hands and roll the mixture into small balls about the size of walnuts (you should get about 18 balls).
Heat a wok until smoking and add 100-150ml groundnut oil. When very hot, add half the meatballs and fry until browned all over. Don’t move them around too much as they will break up. Remove with a slotted spoon and drain on kitchen paper. Repeat with the rest of the meatballs.
Pour all but 1 tbsp of the oil out of the wok. Add the garlic, ginger and chilli and stir fry for 1-2 minutes. Add the onion and green pepper and, keeping the heat high, stir fry for another 2 minutes.
Add the rice wine and allow to bubble off before adding the stock, soy and oyster sauce. Add the meatballs back to the wok. Cover and simmer for 7-10 minutes.
Add the tomatoes and cook, uncovered, for 2-3 minutes or until tomatoes have cooked out slightly and softened. Taste to check the seasoning.