In a large bowl whisk together all the ingredients for the marinade. Reserve some of the marinade for basting later on the grill.
Brush the high heat oil on the mushrooms and the pork. Having placed the hot coals in the center of the grill, arrange the mushrooms just outside the edge of the coals. One to the left, and one to the right. Now place the pork just outside the mushrooms. Both the mushrooms and the pork are receiving a lot of heat while not being directly over the coals.
Grill for 3.5 minutes, baste with the leftover marinade and flip. Grill for another 3.5 minutes, brush with marinade. Flip mushrooms and pork one last time after 7 minutes on the grill, but place the pork directly over the coals, and continue cooking for another 4-5 minutes, or until a thermometer registers 145-160 degrees. This will ensure a slight char while still being moist in the center. Remove pork and mushrooms, and let rest on a plate. Loosely cover with foil.
In a large bowl drizzle a tablespoon of the dressing down the sides. Before it pools in the bottom, place two handfuls of spinach in the bowl. Toss, and plate.
Spoon up to ¼ cup of the barley over the spinach, add the carrots and beets.