There's plenty of room for experimentation here. We've used grilled eggplant, zucchini, bell peppers, and onion sandwiched in crusty rolls with a little pesto. Fennel, endive, or mushrooms would make fine vegetable substitutes; sun-dried tomatoes or white-bean puree can replace the pesto; or omit the condiment altogether and top the sandwich with whole fresh basil or mint leaves. You can even change the cooking equipment, using the broiler or a grill pan in lieu of an outdoor grill.
Slideshow: More Sandwich Recipes