20 Tablespoons of oil!!?? Any alternatives??

Most traditional cakes use about 1 cup of fat (oil or butter). Fat provides tenderness and soft moist texture. You can't really substitute out the fat without changing the entire recipe.

You will have to use another recipe that was designed for use with a fat replacement, like applesauce. In my experience when you take out the fat and replace with applesauce or something else, the cake tends to be dense and gummy. A cake with little fat tends to also be dry.

You can make the recipe as is and enjoy in moderation. Or you look for a recipe that does not have a much oil or butter (fat).

Sorry, but I wouldn't start tinkering with a main ingredient until after I'd made it at least once.
If the amount of oil disturbs you, maybe look for another cake you like better.
If you still want to make this cake, but use less oil, use cooking spray when roasting the squash and omit the glaze.
That leaves 1 cup of oil (16 of the 20 tbsp you noted) to use in the batter.