Portobello philly Cheese Steak Sandwich

Name: Portobello philly Cheese Steak Sandwich
Ingredients: 2 teaspoons extra virgin olive oil; 1 medium onion, sliced; 4 large portabella mushrooms, stems and gills removed (optional); 1 large red bell pepper, thinly sliced; 2 tablespoons fresh oregano, minced or 2 teaspoons dried oregano; 1⁄2 teaspoon fresh ground pepper; 1 tablespoon all-purpose flour; 1⁄4 cup vegetable broth; 1 tablespoon reduced sodium soy sauce; 3 ounces reduced-fat provolone cheese, thinly sliced; 4 whole grain buns, split and toasted