1. To prepare the meatloaf: Remove and discard the tough stems from the mushrooms and then generously brush or spray them with oil. Grill or saute over medium heat until barely tender, 6 to 7 minutes, turning once or twice. When cool enough to handle, cut the mushrooms into 1/4-inch pieces.
2. In a medium bowl combine the bread crumbs and milk, mix well, and let stand while combining the rest of the ingredients. In a large bowl, combine all the meatloaf ingredients, including the mushrooms and soaked bread crumbs. Using your hands, mix the ingredients thoroughly but do not overwork. Form into a loaf about 9 inches long and 5 inches wide. Place the loaf in the middle of a disposable aluminum pan. Grill over indirect medium heat or place in preheated 350 degree oven for 45 minutes.
3. After 45 minutes, brush the barbecue sauce over the top and sides of the meatloaf and continue to grill(bake) until the internal temperature reaches 160°F, 40 to 45 minutes more. Let rest for 5 to 10 minutes. Cut into 1-inch slices and serve warm.