Pre-heat the oven to 200°C.
Toss the pumpkin slices with the olive oil, cumin seeds, paprika and thyme until the pumpkin is well coated. Season with ground sea salt and fresh cracked pepper and transfer to a large roasting tray.
Roast the pumpkin in the hot oven for 15 minutes until soft and golden.
Transfer the roasted pumpkin and all the pan juices to a shallow bowl and drizzle over the lemon juice. Place in the fridge to marinate for at least 30 minutes.
When you are ready to assemble the lasagne cook the pasta sheets in batches in plenty or rapidly boiling water until al-dente (tender) but not overcooked. Crumble the feta into the yoghurt and combine.
Turn down the oven to 180°C.
In a deep pie or lasagne dish spoon in a layer of the feta/yoghurt mix, top with a layer of baby spinach/silverbeet and then a layer of the roasted pumpkin. Top with cooked lasagne sheets.
Top with a couple of spoonfuls of the pureed tomatoes, more feta/yoghurt, baby spinach/silverbeet and pumpkin. Top with another layer of cooked pasta and repeat. Finish by sprinkling the walnuts and parmesan on top, and place in the oven to cook for 35-40 minutes until bubbling and golden on top.
Remove from the oven and allow to cool for a few minutes before cutting into wedges. Serve accompanied with a crisp salad or a side of low-FODMAP vegetables if you prefer.