Place mushrooms in a quart-size zip-top plastic bag. Add vinaigrette; seal bag, and gently toss to coat. Let stand 15 minutes.
. While mushrooms marinate, cut bread loaf in half horizontally. Hollow out top and bottom halves of loaf, leaving a 1/2-inch border. Reserve torn bread for another use.
. Combine cheeses in a small microwave-safe bowl; microwave at HIGH 15 seconds or until soft. Add olives, mustard, and garlic; stir well. Spread mixture on bottom half of loaf; top with basil, tomato, and mushrooms. Top with remaining half of loaf. Coat both sides of sandwich with cooking spray.
. Heat a large nonstick skillet over medium heat; place sandwich in pan. Place a piece of foil over sandwich; top with a heavy skillet. Cook 2 minutes. Turn sandwich; replace foil and heavy skillet. Cook 1 to 2 minutes or until golden brown. Cut into 4 equal portions.