Place the beetroot on a baking tray in a single layer. Drizzle over the oil and season well with salt and freshly ground black pepper. Toss the beetroot to ensure it is evenly coated in the oil, then roast for 30 mins until tender and beginning to turn golden at the edges
Meanwhile, combine the dressing ingredients in a medium bowl and set aside
Once the beetroot is cooked, tip it into the dressing and leave to marinate for 45 mins
Combine the lentils with the rocket, feta, walnuts, and beetroot with dressing and toss until well combined
Tip onto a platter and scatter chives over the top