Heat 1 tablespoon of the oil in a large frying pan; cook onion, stirring, for 5 minutes or until onion softens. Add garlic; cook, stirring, until fragrant. Stir in tomatoes, passata and chilli. Transfer to a medium jug.
2.
Toss eggplant in flour to coat, dust off excess. Heat remaining oil in same pan; cook eggplant, in batches, until browned. Drain on paper towel.
3.
Layer half the eggplant in a 4.5-litre (18-cup) slow cooker; season. Top with half the tomato mixture, basil and bocconcini. Repeat layering, finishing with parmesan. Sprinkle with paprika. Cook, covered, on low, for about 6 hours.