Peel the squash and cut in thin slices (pay attention with knife as the squash is pretty hard).
Roast slices on a hot skillet or grill for a couple of minutes on each side.
In a bowl put blue cheese, breadcrumbs, chopped rosemary needles and hazelnuts, mix with a fork until you have a crumbly dough.
Adjust salt and pepper, you may need less or more breadcrumbs, it depends on how creamy is blue cheese.
Put the squash slices on a baking tray, put a spoonful of crumble on each one, bake for about 15 minutes at 360°F or untill the crumble is crispy.
Serve hot or warm.