Preheat the oven to 400°F.

Wrap the beets in aluminum foil and place them on a baking sheet.

Toss the diced sweet potato with 1 tablespoon of olive oil, 1/2 teaspoon of salt, and black pepper, then spread them out on the baking sheet alongside the beets.

Roast the beets and sweet potatoes in the preheated oven for 30-40 minutes, or until the sweet potatoes are tender and the beets can be easily pierced with a fork.

Remove from the oven and let cool slightly. Once cool enough to handle, peel the beets and cut them into bite-sized pieces.

In a large bowl, combine the mixed salad greens, roasted sweet potatoes, and roasted beets.

In a small bowl, whisk together the Greek yogurt, lemon juice, honey, remaining 1/2 teaspoon of salt, and garlic powder until smooth.

Drizzle the yogurt dressing over the salad and toss gently to combine.

Top with crumbled feta cheese and chopped walnuts before serving.