1. Mix oil, vinegar and Montreal Steak Seasoning in small bowl. Brush both sides of each mushroom cap with oil mixture. Lightly brush one side of each bread slice with oil mixture.
2. Grill mushrooms over medium heat 6 to 8 minutes, turning once. Grill bread slices until lightly toasted.
3. Serve mushrooms between bread slices with assorted garnishes, as desired.