Preheat the oven to 400°F (200°C). Wrap the beets in aluminum foil and place them on a baking sheet. Roast for about 45 minutes or until tender. Allow to cool, then peel and dice.

In a mixing bowl, whisk together the olive oil, balsamic vinegar, honey, minced garlic, salt, and black pepper until well combined.

In a large salad bowl, combine the mixed greens, roasted beets, crumbled feta cheese, and toasted walnuts. Drizzle with the vinaigrette and toss gently to combine.