1 Preheat the oven to 180°C. Line two baking trays with baking paper. Place the pumpkin onto prepared trays; lightly spray with olive oil. Bake for 25–30 minutes, swapping trays halfway through the cooking time.
2 Meanwhile, heat 1 tablespoon of olive oil in a large saucepan over medium heat. Cook onion, carrot and celery, stirring, for 6–7 minutes. Add the garlic and cook, stirring, for 1 minute, or until fragrant. Add tomato paste and cook, stirring, for 1 minute. Add lentils, tomatoes, vinegar and 2½ cups of water, and bring to the boil. Reduce heat to low. Simmer, partly covered, stirring occasionally, for 30 minutes, or until the lentils are tender.
3 Meanwhile, combine ricotta and egg in a large bowl until smooth. Season with cracked black pepper.
4 Lightly spray a 2-litre (8-cup capacity) baking dish with olive oil. Spread one-third of the pumpkin over the base of the dish. Top with half of the lentil mixture and half of the spinach leaves. Repeat with another layer of pumpkin, remaining lentils and spinach. Finish with the remaining pumpkin. Spoon over egg and ricotta mixture, roughly spreading to the edges. Spray the lasagne with oil.
5 Bake in preheated oven for45 minutes. Set aside for about 10 minutes. Drizzle over pesto before cutting into slices. Serve.