Preheat the oven to 200℃ (190℃ fan)/400°F/gas mark 6. Place the hazelnuts on baking sheet and toast for 4-5 minutes until golden. Set aside.
Place 2 tablespoon of the oil in a large bowl with some seasoning, a pinch of chilli flakes and half the garlic, mix together then add the prepared squash and toss so that the squash is well coated in the oil. Tip out onto one end of a large baking tray.
Add 1 tablespoon of oil to the bowl, some more seasoning, chilli flakes and the remaining garlic, then add the beetroot and toss until coated the oil. Tip out onto the other end of the baking sheet.
Finally add the onnion slices to the bowl and swirl around to pick up any of the remaining oil left in the bowl then scatter on top of the squash and beetroot.
Roast in the oven for 30 - 40 minutes or until the vegetables are tender. Allow to cool for a few minutes if serving the salad warm or completely if serving cold. Roughly chop the toasted hazelnuts
Place most of rocket leaves into a serving bowl. Toss in about half of the roasted vegetables and top with half the feta. Add the remaining vegetables, followed by the remaining feta, then sprinkle with the toasted hazelnuts.
Top with the remaining rocket leaves then drizzle with balsamic vinegar and some extra oil before serving.
I used one large baking tray. The squash and beetroot should be spread out in a single layer, so you may need to spread out over two baking trays if yours are smaller.Nutrition information is approximate (does not include seasoning with salt and pepper) and is meant as a guideline only.