Heat your oven to 200C/190C fan/Gas 6.
Cut your squash in half lengthways. Scoop out the seeds. Cut the squash into 3 cm chunks (no need to peel). Chuck on a baking tray. Wrap the unpeeled garlic cloves in a square of foil. Put next to the squash.
Slide the squash into the oven and roast for 30 mins till the squash is soft. The skin will soften during roasting.
Meanwhile, finely chop the sun dried tomatoes and pop in a bowl. Cover with 50 ml boiling water to soften them. Finely shred the cavolo nero.
When the squash has 10 mins left to cook, rub 1 tsp oil into each steak and season. Heat a frying pan over a high heat. Carefully place each steak into the pan. Cook for 3 mins on each side for rare, 5 mins on each side for medium and 6-7 mins on each side for well done.
Remove the steaks and place on a plate to rest. Cover with foil.
Take the squash out of the oven and put in a bowl. Remove the garlic from the tray and use a fork to press the flesh from its skin. Add to the bowl. Add the sun dried tomatoes along with any soaking liquid. Season and mash. Cover with foil.
Put the pan you cooked your steaks in back on the heat. Add ½ tbsp oil. Throw in the rosemary leaves and cavolo nero. Add a pinch of salt and fry for 3 mins. Serve with the rested steaks and sunsquash mash.