The secret for the best pumpkin lasagna you have ever had is to use fresh pumpkin. So cook the pumpkin, mash it to get a pumpkin puree then it to the bechamel sauce and make layers with the other ingredients!
Peel the pumpkin on a cutting board and remove the inner seeds. Then cut it into cubes. You will need to get about 1 kg (2,2 pounds) of pulp from it, net of scraps.
Mash about 2/3 of it with a fork to make a pumpkin puree.
Finish the last layer with plenty of parmigiano. Add on top cubed cooked pumpkin and a few sage leaves