Preheat your oven to 220°C/Fan 200°C/Gas 7. Trim the ends off the squash then halve it. Use a spoon to scoop out the seeds (you can compost them, or toast them with spices for a snack). Chop the squash into bite-sized cubes – no need to peel it unless you want to.
Scrub the potatoes and chop them to match the squash. Peel and thickly slice the red onions. Tumble all the veg into your largest roasting tin (see our tip above). Pour over 2 tbsp olive oil and add some salt and pepper. Toss to coat the veg, then slide them into the oven to roast for 45 mins.
While the veg roast, peel the garlic and finely grate or crush it. Pop it into a medium bowl and pour in 2 tbsp red wine vinegar and 1 tbsp olive oil. Season with salt and pepper. Finely shred the sage leaves, add them to the bowl and whisk together. Drain and rinse the butter beans and tip them into the bowl. Stir and set to one side.
When the veg have roasted for 45 mins, slide the tin out of the oven and carefully turn everything over. The potatoes and squash should be tender and a little charred.
Turn the oven down to 200°C/Fan 180°C/Gas 6. Tip the butter beans into the tin and gently fold them through the roasted veg. Scatter over the breadcrumbs. Slide the tray back into the oven for 10 mins to warm the beans through.
Divide the rocket between 6 plates and top with the roasted veg and beans. Scatter over the chopped hazelnuts to serve.