- 2 teaspoons extra-virgin olive oil
- 1 medium onion, sliced
- 4 large portobello mushrooms, stems and gills removed, sliced
- 1 large red bell pepper, thinly sliced
- 2 tablespoons minced fresh oregano, or 2 teaspoons dried
- ½ teaspoon freshly ground pepper
- 1 tablespoon all-purpose flour
- ¼ cup vegetable broth, or reduced-sodium chicken broth
- 1 tablespoon reduced-sodium soy sauce
- 3 ounces thinly sliced reduced-fat provolone cheese
- 4 whole-wheat buns, split and toasted
- 1 Heat oil in a large non-stick skillet over medium-high heat. Add onion and cook, stirring often, until soft and beginning to brown, 2 to 3 minutes. Add mushrooms, bell pepper, oregano and pepper and cook, stirring often, until the vegetables are wilted and soft, about 7 minutes.
- 2 Reduce heat to low; sprinkle the vegetables with flour and stir to coat. Stir in broth and soy sauce; bring to a simmer. Remove from the heat, lay cheese slices on top of the vegetables, cover and let stand until melted, 1 to 2 minutes.
- 3 Divide the mixture into 4 portions with a spatula, leaving the melted cheese layer on top. Scoop a portion onto each toasted bun and serve immediately.