Heat oven to 200C. Place sweet potato on a baking tray. Drizzle over olive oil, season with salt and pepper and roast for 30 minutes until golden.
Meanwhile, cut aubergine lengthways into thin slices. Brush both sides of the aubergine with olive oil. Lay on a baking sheet, season with salt and pepper and cook for 15-20 minutes.
Cook onion and garlic in a frying pan until soft. Stir through the squash and canned tomatoes, and ½ can water. Simmer for 10-15 minutes. Stir in cooked lentils, sweet potato, a sprinkle of dried oregano, basil leaves and season with salt and pepper.
In a baking dish, add a layer of lentil mix to the bottom of the dish, followed by a sprinkle of the drained tuna chunks on top. Then place a layer of aubergine on top (4-5 slices usually works). Repeat these layers finishing off with the final layer aubergine. Top with mozzarella cheese and season with salt and pepper
Bake in the oven for 15 minutes until golden. Serve with fresh salad leaves.