Grilled Panzanella Salad with Bell Peppers, Summer Squash, and Tomatoes

1 1/2 pounds assorted bell pepper s (about 3 large), cut into 1 1/2-inch-wide strips

1 1/2 pounds assorted summer squash , cut lengthwise into 1/3-inch-thick slices

1 medium-size red onion , cut into 1/4-inch-thick rounds

1 12- to 14-ounce loaf of ciabatta, some crust trimmed to expose bread , cut crosswise into 1-inch-thick slices

Extra-virgin olive oil

1 garlic clove, peeled, cut into thirds Dressing

1/4 cup fresh lemon juice

2 tablespoons red wine vinegar

1 tablespoon grated lemon peel

1/3 cup extra-virgin olive oil

1 pound tomato es, cored, cut into 3/4-inch dice, juices reserved

1/2 cup chopped fresh Italian parsley

1/4 cup coarsely chopped assorted fresh herbs (such as chives , dill, chervil, and tarragon)

2 tablespoons drained caper s