Heat your oven to 200°C/Fan 180°C/Gas 6. Halve the squash and scoop out the seeds (see our tip for what to do with them). Peel it and slice into wedges around 1cm thick. Put in a bowl.
Measure out 1 tsp each of the sumach, fennel and cumin seeds. Add to the squash with a pinch of chilli flakes and 1 tbsp oil. Season. Toss the squash to coat in the oil. Spread out in a large roasting tin. Roast for 20 mins.
While the squash roasts, peel and slice the onion into thick wedges. After 20 mins in the oven, take the squash out and scatter the onion on the tray around the wedges. Slide back into the oven and roast for 10 mins, till the squash and onion are tender.
Tip the quinoa into a sieve and rinse for a few mins. Tip into a small pan. Pour in 150ml boiling water. Add a pinch of salt. Cover. Simmer for 10-15 mins till the water has been absorbed and the quinoa is tender.
Drain the lentils. Rinse and tip into the roasting tin with the squash and onion. Roast for a further 5 mins to warm the lentils through.
While the lentils cook, halve the pomegranate around its middle. Hold one half in your hand, cut-side down, over a bowl. Whack with a wooden spoon. The seeds should tumble out through your fingers into the bowl. Repeat with the other half to get all the seeds out.
Take the roasting tin out of the oven. Add the quinoa, rocket and pomegranate seeds. Season well. Toss to mix. Heap on warmed plates. Serve straight away.