Peel potato and slice into 1/4 inch thick slices. Toss with oil, sugar, vinegar, salt and pepper.
Place in single layer on parchment-lined baking sheet. Bake for 30 minutes or until tender.
Spread fig jam over one side of each slice of bread. Divide sweet potatoes and Le Gruyère slices evenly between sandwiches. Top with remaining slices of bread.
Lightly coat outside of each sandwich with butter. Fry in skillet for 2 to 3 minutes per side or until cheese is melted and outside is golden. Serve immediately.