1 Preheat oven to 180°C. Heat olive oil in large saucepan over medium heat. Sauté onion for 4–5 minutes, or until soft and golden. Add the garlic and cook, stirring, for 30 seconds. Stir in the tomatoes, the stock, lentils, mushrooms and the rosemary. Bring to a simmer. Cook mixture for 10 minutes, stirring occasionally, until reduced and slightly thickened.
2 Meanwhile, set a large non-stick frying pan over medium-high heat. Spray eggplant slices with olive oil. Cook for 2–3 minutes each side. Set aside.
3 Spray a 30 x 21 x 5cm deep ovenproof dish with oil. Lay half the lasagne sheets on the base, breaking or cutting sheets to fit. Spread half of the lentil mixture over. Arrange remaining lasagne sheets over mixture, then spread over the remaining lentil mixture. Arrange eggplant slices on top.
4 Whisk the ricotta, yoghurt, egg and cheese together with a fork. Spread in an even layer over the eggplant. Sprinkle lightly with paprika. Bake for 35 minutes, or until pasta is tender. Stand for 10 minutes, before cutting the lasagne into squares to serve.