Arrange sweet potato slices in a single layer over a baking paper-lined baking tray. Spray with cooking spray. Bake in a 200C oven (fan-forced) for 20-25 minutes, until tender. Cool.
Place kale, lentils and sweet potato in a large bowl. Season with freshly ground pepper and toss gently. Arrange over a large platter. Top with beetroot, feta and walnuts.
To make dressing, place all ingredients in a screw top jar and shake well.
Drizzle dressing over salad to serve.

Reduce prep time by replacing kale leaves with 175g of any packaged, chopped leafy salad mix.
Sweet potato can be microwaved instead of roasted, if preferred. Place slices over base of a large microwave-safe dish, overlapping slightly. Cover with damp paper towel and microwave on High for about 6 minutes, or until tender. Drain and cool.
To toast walnuts, spread over a baking tray and bake in 160C oven (fan-forced) for 5-6 minutes.
Salad (without dressing) can be assembled up to 3 hours ahead. Keep, covered in the fridge. Drizzle with dressing just before serving.
For a warm, non-vegetarian salad, lentils can be replaced with 300g lean lamb or beef steaks. Grill or panfry steaks in a non-stick pan until cooked to your liking. Rest 5 minutes then slice thinly. Arrange over salad.