Rub the turkey with the oil, salt, pepper and sage and place it in a roasting pan with 1 cup broth.
Roast at 350°F for 65 to 80 minutes until the center reaches 165°F, then rest for 15 minutes and slice thinly.
Pour the pan juices into a measuring cup and skim away excess fat.
Melt the butter in a saucepan, stir in the flour for 1 minute and whisk in the pan juices plus enough gravy broth to equal 2 cups; simmer for 5 minutes.
Toast the bread lightly, cover each slice with turkey and spoon the hot gravy over the open-face sandwiches.