Preheat oven to 400 degrees F (200 degrees C).
In a saucepan over medium heat, combine 4 large chopped tomatoes, 2 minced garlic cloves, 1/4 teaspoon salt, zest of 1/3 lemon, and 1 teaspoon brown sugar.
Cook the mixture, stirring constantly, until tomatoes release their juices, about 5 minutes. Then, reduce heat to low.
Cut the ciabatta bread loaf into 2 or 3 pieces per half. Place them cut-side up on a baking sheet.
Bake the ciabatta bread in the preheated oven until golden brown.
Meanwhile, add the juice of 1/3 lemon, 2 tablespoons of olive oil, and black pepper to taste into the tomato mixture.
Cook the tomato mixture uncovered over medium heat until it thickens, about 6 to 8 minutes. Then, remove from heat.
Spread the tomato sauce over the sliced bread and serve hot.