I love this with the Thanksgiving turkey especially, but you can substitute lard or any pan drippings in for the turkey drippings.
Place cucumbers and onions in a bowl. Sprinkle with a small amount of salt, and let stand for about 3 hours to "sweat."
Stir pan drippings and flour over medium heat until it starts to turn golden. Slowly add vinegar, water, sugar and pepper. Bring to a boil.
Squeeze water out of cucumbers and onions, and add them to the gravy mixture. Bring to a boil again, and let simmer for an additional 5 minutes, stirring occasionally.