Preheat oven to broil, keeping the ranch about 6 inches from heating element.
Whisk together oil, vinegar and Dijon for the vinaigrette. Season with pepper.
Brush cut sides of bun halves with vinaigrette and toast lightly under broiler, about 4 minutes; set aside
Remove mushroom gills with a spoon. Wipe them of with a wet paper towel, then brush mushrooms with vinaigrette and place topside up on a pan; broil for about 6 minuets on each side. You want the mushrooms pretty soft, the remove from oven.
Pulse salami, olives and cheese in a food processor until finely chopped and mixed. Take mixture and place in a microwave safe dish, then add the rest of the vinaigrette to it. Microwave about 1 minute until mixture is warm. Divide the mixture between the 4 mushrooms; then return to the oven and broil until the cheese starts to melt and brown. About 5 minutes.
Place the mushrooms on the browned buns and serve.
-If you think provolone cheese is too strong, a swiss would work really well too.