Sorry, I have no recipes but if you are a fairly confident baker whiff you could try a carrot cake and just substitute some pumpkin? I think that would work pretty well.
Batter -type cakes are easy and will take pretty much anything. I use butter but don't see why you can't use a buttery spread. I made a Gluten Free one last week with ground almonds and mashed potatoes, butter, dried fruits, nuts and honey and it was delicious! It was along the lines of a spiced Dundee cake.
I'm a bung-it cook though and don't look for perfection- just something quick and tasty.
I hope someone comes along if you don't want to risk it.