Preheat oven to 400°F (200°C). Wrap beets in foil and roast for 45-60 minutes. Let cool, peel, and cut into wedges.
Whisk together olive oil, balsamic vinegar, honey, mustard, salt, and pepper for the dressing.
In a large bowl, combine greens, roasted beets, onion, goat cheese, and nuts. Drizzle with dressing and toss.
Serve immediately, garnishing with extra goat cheese and nuts if desired.