01 - Preheat your oven to 400°F.
02 - Individually wrap each trimmed beet in aluminum foil. Place them on a baking sheet and roast for 40 to 45 minutes, or until easily pierced with a knife. Allow to cool slightly before carefully peeling the skin and cutting the beets into wedges or cubes.
03 - While the beets are roasting, toast the walnut halves in a dry skillet over medium heat for 3 to 4 minutes, stirring frequently until aromatic. Set aside to cool.
04 - In a small bowl, thoroughly whisk together the extra-virgin olive oil, balsamic vinegar, Dijon mustard, honey, salt, and freshly ground black pepper until well combined and emulsified.
05 - In a large mixing bowl, combine the mixed salad greens, roasted beets, thinly sliced red onion, and toasted walnuts. Drizzle with the prepared dressing and toss gently to ensure all ingredients are evenly coated.
06 - Transfer the assembled salad to a serving platter or individual plates. Garnish with crumbled feta cheese and, if desired, freshly chopped parsley. Serve immediately.