2.Place potato in a single layer on a large lightly oiled oven tray; drizzle with 1 tablespoon of the oil, then sprinkle with 2 teaspoons of the oregano. Season. Turn potato slices to coat evenly. Bake for 30 minutes or until browned; set aside.
3.Meanwhile, cut 3 of the eggplants lengthways into 1cm (½in) thick slices. Place eggplant in a single layer on two trays. Brush eggplant with 1 tablespoon of the oil; scatter with 1 teaspoon of the oregano, then season. Working in batches, cook eggplant slices on a heated chargrill plate (or chargrill pan or barbecue) for 5 minutes on each side or until browned and tender. Transfer cooked eggplant to baking-paper-lined trays.
4.Place lentils and 1 litre (4 cups) water in a medium saucepan; bring to the boil. Reduce heat to low; cook for 15 minutes or until lentils are tender. Drain, rinse under cold water; drain well.
5.Cut remaining eggplant into 2cm (¾in) pieces. Heat remaining oil in a large heavy-based saucepan; cook onion and garlic for 4 minutes or until soft. Add chopped eggplant; cook for 5 minutes or until soft and golden. Stir in carrot and capsicum; cook for 4 minutes. Stir in passata and ½ cup (125ml) water, the thyme and remaining oregano. Reduce heat to low; cook, covered, for 7 minutes or until eggplant is soft. Stir in drained lentils; season to taste.
6.Make ricotta bechamel. Whisk ingredients in a medium bowl until smooth.
7.Arrange potato slices in a single layer in an oiled 3 litre (12-cup), 22.5cm x 36cm (9in x 14½in) ovenproof dish; top with half the lentil mixture, then half the eggplant slices, placing them in a single layer. Repeat layering with remaining lentil mixture and remaining eggplant slices. Spoon ricotta bechamel on top; top with fetta and mozzarella, then drizzle with a little more oil. Bake for 55 minutes or until heated through and top is golden. Stand for 10 minutes before serving.
8.Serve half the lentil bake topped with extra thyme leaves. Transfer remaining lentil bake to an airtight container; cool, then store.
Serve with simple green salad (page 217) or lemony lettuce wedges , if you like.
Refrigerate lentil bake for up to 3 days. Freeze for up to 3 months; thaw in the fridge, then reheat in a microwave.