Cook the pumpkin in a large saucepan of boiling water for 5 mins or until just tender. Drain well.
Meanwhile, place the silverbeet in a large saucepan over high heat. Cook, covered, turning occasionally, for 5 mins or until just wilted. Remove from heat. Set aside to cool slightly.
Use your hands to squeeze as much liquid from the silverbeet as possible. Coarsely shred silverbeet and place in a large bowl. Add the pumpkin, ricotta, parmesan, pine nuts and sage and stir until combined.
Heat oil in a large deep ovenproof frying pan or flameproof casserole dish over medium heat. Add the onion and garlic and cook, stirring, for 5 mins or until onion softens. Stir in the diced tomato, sugo or passata and cream. Bring to a simmer and cook for 5 mins or until the sauce thickens slightly. Season. Remove from heat.
Place 1 lasagne sheet on a clean work surface. Arrange one-sixth of the zucchini ribbons in a single layer over lasagne. Cut in half crossways. Spoon some of the ricotta mixture along 1 short side and roll up to enclose filling. Use a small serrated knife to cut into thirds crossways. Arrange rolls, cut-side up, over tomato mixture in the pan or dish. Continue with remaining lasagne sheets, zucchini and ricotta mixture, arranging rolls side-by-side in tomato mixture.
Preheat oven to 200°C. Cover the pan or dish with foil. Bake for 20 mins or until heated through. Remove foil. Sprinkle with breadcrumbs and cheddar. Bake, uncovered, for 10-15 mins or until golden brown.