Heat the oil to 180C in a large saucepan. The oil shouldn’t come more than halfway up the sides of the pan.
Cut 12, 1.5 centimetre squares from the mozzarella and grate the rest.
Cut the onions in half and top and tail them, and remove the outer skin. Slice thinly, length-ways.
Mix the gram flour, rice flour, spices together. Add the sliced onions, chillies, curry leaves and grated mozzarella and mix all together. Add a few tablespoons of water so that the flours stick to the vegetables.
Take a spoonful of the mixture and put a square of mozzarella on it, then top with more bhaji mix so the cheese is covered. Gently drop it into the hot oil. Add one or two more bhajis depending on the size of your pan: don’t crowd it. Cook for a few minutes until golden brown, turning occasionally if needed. Drain on kitchen paper while you cook the rest.