Prepare the meatballs. Mix together all the ingredients in a bowl and season. Knead the mixture well, then roll cherry-sized pieces into firm balls.
Heat the oil and butter together in the base of a tagine or large, heavy-based saucepan over a medium heat, stir in the onion, garlic, ginger and chilli and cook for 2–3 minutes to let the flavours mingle.
Add the turmeric and pour in the measurement water. Bring to the boil, then drop the meatballs carefully into the liquid. Reduce the heat, cover and cook gently for 25–30 minutes.
Stir in half the coriander, season with salt and pepper and place the lemon segments among the meatballs. Re-cover and continue to cook gently for about 40 minutes. Garnish with the rest of the coriander and serve with plain couscous, if liked.