Place a sheet of foil on a baking pan. Rub the olive oil all over the mushroom, then sprinkle both sides with salt & smoked paprika. Roast at 425 for about 20-25 minutes.
Meanwhile, make the olive salad. In a small bowl, combine the green olives, Kalamata olives and chopped giardiniera until the mixture is uniform. Set aside.
I like to assemble this upside down: Spoon about ¼ cup of the olive salad mixture onto the top slice of bagel. Top with roasted red pepper slice, followed by provolone cheese slices.
Finish it off by placing the cooled portobello on top, then topping with the "bottom" piece of the bagel. Hold firmly, then flip & cut in half or into quarters if serving as an appetizer.