Combine the lentils and stock in a large saucepan, cover with the lid, and bring to the boil over a medium–high heat. This should take 7–8 minutes. Reduce the heat and keep at a steady simmer with the lid ajar for 15–20 minutes. Remove the lid for the last 5 minutes of cooking time to evaporate the remaining water. The lentils should be cooked but with a slight bite, so test them along the way – you don’t want mushy lentils in the salad.
Meanwhile, place the butternut squash in a large roasting pan and drizzle over the light olive oil. Season generously with salt and pepper and use your hands to toss, coating the squash evenly. Bake in the middle of the oven for 8–10 minutes. Remove the squash from the oven and turn the pieces over, then toss in the onion wedges, coating them with some of the cooking oils. Bake for a further 10–12 minutes or until cooked.
Remove the squash and onions from the oven and let rest for 6–7 minutes. If necessary, drain any excess water from the cooked lentils then gently toss them through the baked vegetables. Toss through the pickled beetroot, feta and rocket. Serve on a large plate, drizzled with the lemon juice and extra virgin olive oil and sprinkled with the toasted pumpkin seeds.