Take pumpkin and cut off top. Slice in half and scoop out the insides, reserving seeds for roasting. Cut each side in half and from there, cut each quarter of pumpkin into 1" strips. Continue to cut pumpkin in to 1" cubes and slice off shell on each piece. Cut pumpkin pieces in to 1/2" pieces.
Dice the onion and toss with 2-3 cups pumpkin and olive oil. Roast for 20-25 minutes or until pumpkin is beginning to brown and is tender.
While pumpkin roast, stir together ricotta, egg white, salt, and pepper. Set aside.
Bring a pot of water to a boil and cook lasagna noodles until tender.
In a small sauce pan, heat butter over medium-low. Once melted, whisk in flour and cook for 1 minute. Whisk in milk and continue to cook until sauce has thickened. Remove from heat and stir in blue cheese.
To assemble lasagna, pour 1/4 of the blue cheese sauce at the bottom of an 9 x 6 pan. Layer lasagna noodles on top followed by 1/2 the ricotta, 1/2 the pumpkin mixture, and another 1/4 of the blue cheese sauce. Repeat once more and for the final layer, add lasagna noodles, the remaining blue cheese sauce, and finish with mozzarella cheese.
Bake for 20-25 minutes. Cheese on top should be lightly browned.
Notes
*I bought my 9 x 6 pan at Crate and Barrel (because it feeds 2 just right!) You can always do 1/2 times the recipe for an 8 x 8 pan- you should still only need one pumpkin.