Place butternut squash halves on a large baking sheet flesh side up. Roast in the oven for 50 to 60 minutes at 200°C, until flesh is fork-tender, then remove from the oven.
Meanwhile, cook the onion and thyme on a medium-low heat in olive oil for 5 minutes, stirring occasionally. Stir in the frozen spinach, cover with a lid and allow to slowly cook for another 15 minutes, or until the liquid has evaporated, then remove from the heat.
Discard the squash skin and mash up the flesh with a fork. Keeping them separate, season both the squash and spinach with salt, pepper and a grating of nutmeg.
Make the sauce: fry the garlic, over medium heat, in olive oil for a couple of minutes, or until lightly golden. Pour in the puree, bring to the boil, simmer for just 3 minutes, season with salt and pepper. Transfer the sauce to an ovenproof dish.
On a clean work surface, lay out the pasta sheets facing lengthways away from you. Working quickly so your pasta doesn’t dry out, brush them with water, then evenly divide and spread the squash over the sheets.
Sprinkle over the cooked spinach and crumble over the feta. Roll up the sheets and cut each one into 3 - 4 chunks.
Place rotoli side by side in the tomato sauce, sprinkle with grated Parmesan and little olive oil. Cover with Alu foil and bake in the oven at 180°C for 35 - 40 minutes until golden and crisp. Remove the foil halfway through.