So simple, so delicious...

 Burger on wheat kaiser roll with avocado, smoked mozzarella and balsamic reduction.

The onion rings are also drizzled with the reduction.

One of the delicious things we had when we ate at Robert Irvine's restaurant was the balsamic reduction we had with the bread and drizzled over the fried green tomatoes.  We were having burgers one night last week and I asked Ben what gourmet direction he wanted to take them using the nice piece of smoked mozzarella I had on hand.  Without hesitation he said he wanted them drizzled with a balsamic reduction, some balsamic reduction it was (so fortunate too, that I has an unopened bottle of balsamic vinegar in the pantry).  I simmered the bottle (in a nonreactive pan, of course) until it was reduced by about 3/4, with a nice syrupy consistency.  This did take a while and you have to be careful not to inhale the fumes directly, but it was simple and only required that I check it occasionally to make sure that it did not burn.  What was left I put into a plastic condiment bottle and stored back in the pantry to use later. I would highly recommend giving this a try, even if it means going out and buying a (moderately priced) bottle just for this purpose.

Same burger (mine), with the addition of tomato.