Preheat the oven to 400°F (200°C). Wrap the beets in aluminum foil and place them on a baking sheet. Roast the beets in the preheated oven until they are tender, about 45 minutes. Allow them to cool before peeling and slicing.
While the beets are roasting, toast the walnuts in a dry skillet over medium heat until they are fragrant, about 5 minutes. Set aside to cool.
In a small bowl, whisk together the olive oil, balsamic vinegar, honey, salt, and black pepper to make the dressing.
In a large bowl, combine the mixed greens and sliced beets. Drizzle with the dressing and toss gently to combine.
Top the salad with crumbled goat cheese and toasted walnuts before serving.