Place the bell peppers and eggplant on a baking sheet and roast, turning several times to cook evenly, until the peppers are blistered and blackened all over and the skin of the eggplant is wrinkled and shriveled, about 45 minutes. Transfer the peppers and eggplant to a paper bag. Close the bag and set aside until cool enough to handle, about 15 minutes. Leave the oven on.
Peel the charred skins off the roasted vegetables. Slice each bell pepper in half lengthwise and discard the seeds, ribs and stems. Cut the peppers and eggplant into thin strips.
Meanwhile, make the dough: In a bowl, sift together the flour, salt and baking powder. Make a well in the flour and add the olive oil and egg yolk. Gradually add the water, mixing the wet ingredients into the flour little by little with a wooden spoon. Turn the dough out onto a lightly floured board and knead until soft, smooth and elastic, about 1 minute. Form the dough into a ball and place in a large, lightly oiled bowl. Cover with a kitchen towel and let stand in a warm place until the dough puffs slightly, about 30 minutes.
In another large bowl, combine the eggplant and bell pepper strips with the garlic and olives, and season generously with salt and pepper.
Lightly oil a 12-by-9-inch rimmed baking sheet. On a lightly floured work surface, roll out the dough into a rectangle to fit the pan. Press into the prepared pan and trim away any excess dough.
Cover the dough base with the tomato slices. Drizzle 2 Tbs. of the olive oil over the tomato slices. Arrange the eggplant mixture evenly over the tomatoes and drizzle with the remaining oil.
Bake until the edges are beginning to brown, about 25 minutes. Remove from the oven and let cool slightly. Cut into squares and serve warm.
Adapted from Williams-Sonoma Foods of the World Series, Barcelona, by Paul Richardson (Oxmoor House, 2004).