Put the pumpkin and butter in a saucepan with 5 tablespoons of water. Cover and cook for 15 minutes until the pumpkin is tender.
Mash with the nutmeg and grated parmesan; reserve.
Boil a saucepan of water with a generous pinch of saffron and some salt for 5 minutes.
Fry the mushrooms in the remaining oil. When they are nearly cooked add the garlic so it browns and crisps but doesn't burn.
Wilt the spinach in the microwave or a saucepan for approximately 1 minute.
Add the lasagne in the boiling saffron water for 1 minute until just tender then drain.
Take 2 warm plates and put a layer of spinach just slightly smaller than the lasagne on the bottom. Top with a square of lasagne, then a spread over a spoonful of pumpkin, then add a few spinach leaves and then another square of pasta. Continue this until you have 4 layers of lasagne then top off with a spoonful of pumpkin.
Scatter round the garlic mushrooms then spoon over the dressing or you could put this in a serving jug and allow guests to do their own. Top off with parmesan shavings.