1. Preheat the oven to 200°C / 400°F / Gas Mark 6. Drain the salmon, removing the skin and bones if desired and break the salmon into large chunks. Cover and set aside
2. Split the ciabatta loaf in two through the middle. Place the bread, cut sides up, on a baking sheet. Sprinkle with 2 tablespoons of the olive oil, and the dried rosemary. Bake for 5 - 6 minutes
3. Meanwhile, heat the butter with the remaining olive oil in a frying pan. Add the onion and cook until softened and browned
4. Remove the ciabatta from the oven. Arrange the salmon chunks on top, then scatter with the onions. Return to the oven for a couple of minutes, then cut each piece in half. Serve, sprinkled with the parmesan shavings and basil leaves, and seasoned with black pepper.