Wash and dry all produce. Preheat oven to 400 degrees. Halve the potatoes. Halve, peel, and chop onion into 1/2-inch wedges. Strip thyme from stems and discard stems. Roughly chop leaves.

Toss potatoes, onion, thyme, a large drizzle of olive oil, and a pinch of salt and pepper on a baking sheet. Roast in oven until browned and tender, about 25 minutes. Toss halfway through.

In a small pot, add lentils, stock concentrate, and enough water to cover by 1 inch. Bring to a boil over mediumhigh heat, then lower heat and reduce to a simmer. Cook until tender, about 20 minutes. Drain, then season with salt and pepper.

Meanwhile, cut beets into 1/2-inch wedges. Mix together honey and 1 TBSP balsamic vinegar (we’ll be using the rest later) in a large bowl. Add beets and toss to coat. Season with salt and pepper. With 5 minutes to go on the potatoes and onion, add beets to baking sheet and roast together for the last 5 minutes.

When veggies are done roasting, add them to same large bowl along with the lentils, a large drizzle of olive oil, and remaining balsamic vinegar. Toss until combined. Gently mix in arugula. Season with salt and pepper.

Divide salad between plates. Sprinkle with feta cheese and walnuts before serving.