Peel and cut the squash into 2cm cubes.
Chop the rosemary leaves. Thinly slice the spring onions.
Heat the oil in a large, non-stick frying pan and add the rosemary and squash cube. Fry them for about 10 minutes, stirring regularly. Season with salt and pepper.
When they are soft and golden, add the garlic and chilli flakes. Stir for 2 minutes, then add the balsamic vinegar and keep stirring gently for a minute or so, until they get sticky and slightly caramelised.
Meanwhile, cut the ciabatta rolls in half, put them on a baking tray, drizzle them with oil and put it in the oven. Bake or grill until golden. (Alternatively, you can toast them in a toaster.)
Take about third of the squash into a bowl and mash them roughly with a fork.
Spread this onto the toasted ciabatta rolls, then top them with the caramelised squash cubes and the spring onion slices. You can crumble some cheese on top too, if preferred.
Scatter a few coriander, mint, basil or parsley leaves on top, then serve.