01 - Set the oven to 400°F to prepare for roasting the beets.
02 - Individually wrap each beet in aluminum foil and arrange on a baking sheet. Roast for 40 to 50 minutes until tender when pierced.
03 - Allow roasted beets to cool until manageable. Peel off skins and cut into wedges or bite-sized pieces.
04 - Combine olive oil, balsamic vinegar, Dijon mustard, honey, salt, and pepper in a small bowl. Whisk until emulsified.
05 - In a large bowl, toss arugula, roasted beets, and sliced red onion with the dressing until evenly coated.
06 - Transfer salad to a serving dish. Garnish with crumbled feta and toasted walnuts. Serve immediately.