Crumble the sausage into a saucepan over low heat; cover and cook until sausage is completely browned, stirring every 30 seconds; drain.
Place the bread on a baking tray with the crust sides down. Arrange the cooked sausage evenly over both halves of bread. Top each with tomato slices, red capsicum strips, mozzarella slices, green olives, and black olives.
Bake in preheated oven for 10 minutes.
Whisk together the olive oil, balsamic vinegar, oregano, basil, salt, pepper, onion, and garlic in a bowl. Drizzle over baked bread halves.
Bake another 5 minutes. Cut into 5cm slices to serve.