In a saucepan over medium heat, stir together tomatoes, garlic, salt, lemon zest, and brown sugar. Cook, stirring constantly, until tomatoes release their juices, about 5 minutes. Reduce heat to low.
Cut each half of ciabatta into 2 or 3 pieces. Place cut-side up on a baking sheet, and bake in preheated oven until golden brown.
Meanwhile, stir lemon juice, olive oil, and pepper into the tomato mixture. Cook, uncovered, over medium heat until mixture is thick, about 6 to 8 minutes. Remove from heat, and spread tomato sauce over sliced bread. Serve hot.
