Preheat the oven to Gas Mark 7, 220°C, fan 200°C. Scatter the squash, onion wedges and chopped sage in a large nonstick roasting pan that is big enough to take them in a single layer. Drizzle over 2 tablespoons of the oil and toss everything to coat. Tuck the sausages in among the vegetables, then brush with the remaining tablespoon of oil. Roast for 20 minutes, then give everything a quick stir and roast for a further 10-15 minutes, or until the sausages are brown and the vegetables are turning golden at the edges.
Meanwhile, heat a little oil in a small pan (enough to just cover the bottom of it). When the oil is hot, drop in a handful of whole, dry sage leaves and fry for a few seconds, until just crisp. Remove with a slotted spoon and drain on kitchen paper.
Scatter the fried sage leaves over the roasted sausages and vegetables. Serve with the green veg of your choice.
To prepare the squash, halve it by cutting from top to bottom along the middle with a sharp knife. Hold it steady with one hand and remove the skin with a vegetable peeler, before scooping out the seeds with a spoon.
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