Cook bacon in a nonstick skillet, and reserve 1 Tbs of the bacon grease. Set bacon aside on paper towels, and break pieces in half.
Cook onions in the bacon grease, for about 3 minutes. Add balsamic vinegar and cook 2 minutes more.
While onions are cooking, butter one side of each slice of bread and place butter side down in skillet, on medium heat.
While in the skillet, top one slice of bread with Strawberry Jalapeño spread, and the other with cheese, bacon, and caramelized onions.
Put sandwich together and grill bottom is golden brown. Flip after 4-5 minutes and continue to cook until cheese is melted and both sides of the bread are golden.