Heat 1 tablespoon of the oil in a large frying pan and fry the onion and leek for 5 minutes. Stir in the aubergine and carrot and cook for a further 10 minutes. Remove from the heat, tip into a bowl and mix with the parsley, cheddar and 175g of the breadcrumbs until combined.
Put the flour on a plate, the egg in a bowl and the remaining breadcrumbs on another plate. Using your hands, mould the veg mixture into 12 small logs. Roll each one in the flour, then dip in the beaten egg and finally roll in the breadcrumbs to coat.
Heat the remaining oil in a frying pan and fry the croquettes for 5 minutes, turning, until crisp and golden. You may need to do this in batches. Garnish with parsley and serve with salad and tzatziki on the side.