For cranberry relish, in a large skillet heat oil; cook cranberries and onion in the hot oil over medium heat for 5 minutes or until just softened, stirring often. Stir in vinegar; cook and stir about 1 minutes more or until most of the liquid is absorbed; let cool.
Split loaf of bread in half horizontally. Hollow out inside of each half, leaving a 3/4-inch-thick shell. Arrange cheese slices on the bottom half of the bread. Spoon cranberry relish over cheese. Layer meat and lettuce on top of relish. Spread mayonnaise on the cut side of the top half of bread; place spread side down on filled loaf. Cut sandwich into wedges.