- 1 1/2 lb red bell peppers (3 large), halved lengthwise
- 1 1/2 lb yellow bell peppers (3 large), halved lengthwise
- 5 tablespoons extra-virgin olive oil plus additional for oiling pan
- 1/2 cup finely chopped fresh flat-leaf parsley
- 1 tablespoon finely chopped fresh thyme
- 1/2 teaspoon finely chopped fresh rosemary
- 1 teaspoon finely grated fresh lemon zest
- 1 1/2 teaspoons salt
- 3/4 teaspoon black pepper
- 3 1/2 cups cubed (1/2-inch) baguette (preferably sourdough; from 1 loaf)
- 1 oz finely grated Parmigiano-Reggiano (1/2 cup)
- 4 large yellow tomatoes (2 lb total), cored and each cut crosswise into 5 slices
- 4 large red tomatoes (2 lb total), cored and each cut crosswise into 5 slices
- Special equipment: a 13- by 9-inch (3- to 31/2-qt) gratin or nonreactive shallow baking dish (see cooks' note, below)
- Preheat broiler.
- Arrange bell peppers, cut sides down, in a shallow baking pan.
- Broil 4 to 5 inches from heat until blackened and beginning to soften, about 15 minutes.
- Cover pan tightly with foil and let stand, covered, until cool enough to handle, 10 to 15 minutes. 3Peel peppers and cut lengthwise into 1/2-inch-wide strips.
- Put oven rack in middle position and preheat oven to 400°F. Lightly oil gratin dish.
- Stir together parsley, thyme, rosemary, zest, salt, and pepper in a bowl. Toss bread cubes with cheese and oil (5 tablespoons) in another bowl.
- Arrange half of tomatoes in gratin dish, overlapping slices and alternating colors, then spread half of pepper strips on top. Sprinkle with half of herb mixture and 2 cups bread mixture. Repeat layering with remaining ingredients, ending with bread mixture.
- Bake gratin until vegetables are bubbling and topping is golden brown, 35 to 45 minutes, covering dish with foil if bread browns too quickly.
- Cool gratin on a rack to warm or room temperature.