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). Slice into wedges around 3cm 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 on a baking tray. 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 30 mins till the squash and onion are tender and a little charred.
Halve the pomegranate around its middle. Hold one half in your hand, cut-side down. Whack with a wooden spoon over a bowl. The seeds should tumble out. Repeat with the other half to get all the seeds out.
Drain the lentils. Rinse and tip into a pan with a few spoonfuls of water. Gently heat for 2-3 mins till warmed through. Drain well.
Add the lentils and rocket to the pomegranate seeds. Season well. Toss to mix. Heap on warmed plates. Top with the roast squash. Serve straight away.