Heat the oil in a saucepan, add the pumpkin and sweat over low heat until they start to soften. Add the garlic and 1/2 cup water, then cover and cook over low heat for about 10 minutes or until pumpkin is tender. Drain, cool slightly, then place in a food processor with the sage, nutmeg, salt and pepper. Process until smooth, then place in a bowl with the cottage, and spinach.
Preheat the oven to 180°C Grease a 20 x 27cm ovenproof dish.
To make the sauce, melt the margarine in a saucepan over low heat. Add the flour and cook for 2 minutes, stirring constantly. Add the milk, edam cheese and sage, whisking well until smooth. Cook over very low heat until thickened. Stir in 1/4 cup walnuts and season with salt and pepper.
Place a portion of the mixture in the middle of each lasagna piece. Roll up to enclose. Place seam side down in the dish. Pour half the sauce into dish, then sit the filled tubes on top. Cover with the remaining sauce and sprinkle with the remaining parmesan. Bake in the oven for 30 minutes or until golden. Serve garnished with the remaining walnuts.