In a separate bowl, mix the canned diced tomatoes with some salt and pepper. This sauce will be the base of the lasagna.
In a bowl, combine the ricotta with 100 g of the grated parmesan. This mixture will go between the layers of the lasagna.
Start with a layer of tomato sauce on the bottom of a baking dish. Place a layer of lasagna sheets on top, followed by the pumpkin-spinach mixture. Then add the ricotta mixture and some mozzarella slices. Repeat the process until all ingredients are used up. The final layer should be mozzarella and the remaining parmesan.
Preheat the oven to 180 °C (fan). Cover the baking dish with aluminum foil and bake the lasagna for about 30 minutes. Then remove the foil and bake for another 15-20 minutes until the cheese is golden brown and bubbling.
Allow the lasagna to rest for about 10 minutes before serving so it can be cut more easily.