Grilled Vegetable and Mozzarella Sandwiches

INGREDIENTS

• 3 cups (1/8-inch-thick) diagonally cut zucchini (about 1 pound)
• 3 (1/8-inch-thick) slices red onion
• 1 red bell pepper, seeded and cut into 4 pieces
• 2 tablespoons balsamic vinegar
• 1 teaspoon extravirgin olive oil
• 1/2 teaspoon salt
• 1/4 teaspoon freshly ground black pepper
• Cooking spray
• 1 (1-pound) loaf ciabatta, cut in half horizontally
• 1 cup gourmet salad greens
• 5 ounces fresh mozzarella cheese, sliced
• 8 fresh basil leaves