Stir sugar into lukewarm water in a large bowl. Sprinkle yeast over the top. Leave until foamy, about 5 minutes. Stir to dissolve yeast.
Reserve 2 tablespoons of chopped parsley to garnish the bread. Stir the remaining parsley, 3 tablespoons oil, salt and sage into the yeast mixture. Add 2 cups flour; mix vigorously. Stir in 3 cups flour to make a stiff dough.
Lightly flour a work surface. Knead the dough until smooth and elastic, about 10 minutes; add more flour as needed to prevent sticking. Shape the dough into a ball. Place the dough in a lightly oiled bowl, turning to coat all sides. Cover loosely with plastic wrap. Leave to rise in a warm place until doubled in volume, about 1 hour 15 minutes.
Lightly oil a 43x28 cm Swiss roll pan. Punch the dough down and knead it briefly. Pat the dough into a rectangle and place the dough in the oiled pan, patting to fit. Cover the dough loosely with plastic wrap. Leave to rise in a warm place until doubled in volume, about 40 minutes.
Preheat oven to 200ºC. Place an oven rack in lowest position. Wet or oil your fingers and make dimples in the dough using your fingertips. Brush with remaining oil. Sprinkle with garlic and arrange tomato slices over the top. Top with capsicum. Sprinkle with Parmesan.
Bake on the lowest oven rack until browned at the edges, 35 to 40 minutes. Transfer to a wire rack. Sprinkle with the reserved parsley. Leave to cool for at least 20 minutes before slicing.