Start the charcoal for the grill.  When the coals are ready, place the fish on the grill and put the lid on the grill. Turn the fish and finish cooking to the desired doneness.  When you put the fish on the fire, start the Caper Sauce.  Combine the capers and wine in a skillet over high heat and bring to a vigorous boil.  Let the wine cook until reduced by half.  Add the butter 1/4 stick at a time while whisking constantly, allowing the butter to melt after each addition.  Add salt and pepper to taste.  Just before the fish comes off the fire, start the spinach.  Cook the garlic in the olive oil over high heat until the garlic just begins to turn brown.  Add the spinach and stir-fry until the spinach just wilts.  Lay out a bed of spinach on each plate.  Place a salmon steak on top of the spinach.  Top with Caper Sauce and serve.