Heat the butter and sauté the onions for approx. 3 mins. then add the garlic and cook briefly. Add the spinach and continue to cook for approx. 3 mins., allow to cool a little. Mix the pumpkin, feta, Parmesan and sage with the spinach, season.
Heat the butter, add the flour and cook over a medium heat while stirring with a whisk; the flour must not take on any colour. Remove the pan from the heat. Pour in the milk, bring to the boil while stirring, then reduce the heat, Simmer the sauce over a medium heat for approx. 10 mins., stirring occasionally until the sauce is thick and creamy. Stir in the cheese, season.
Place 3 lasagne sheets in the prepared dish. Completely cover the pasta sheets with 1/3 of the sauce. Top with half of the vegetables. Repeat. Cover with the remaining 3 lasagne sheets and pour over the remaining sauce. Scatter the cheese and pumpkin seeds on top.
Gratinate for approx. 35 mins. in the lower half of an oven preheated to 200°C.