Preheat the oven to 200°C. In a large pan, over medium heat cook onion for 1-2 minutes. Add carrot and garlic and cook for 1 minute. Add passata and stock.
Simmer gently for 15 minutes until vegetables are cooked. Stir in lentils and season, and then transfer to a baking dish. Meanwhile, cook sweet potato and pumpkin in boiling salted water until tender.
Drain and mash. Stir in butter. Spread over lentil mixture and roughen top with a fork. Bake for 15 minutes or until bubbling and golden.
Serve with a green side salad x