4 portobello mushrooms (about 10 ounces) |
4 (1/2-inch-thick) slices peeled eggplant (about 8 ounces) |
1/4 cup balsamic vinaigrette (such as wish-bone), divided |
1/4 cup chopped bottled roasted red bell peppers |
2 tablespoons chopped fresh basil |
4 (1/2-ounce) slices provolone cheese |
4 (2-ounce) onion rolls, halved |
1/2 cup spinach leaves |