01 - Preheat the oven to 400°F.
02 - Individually wrap each beet in aluminum foil and place on a baking sheet. Roast for 40 to 50 minutes until tender when pierced with a knife.
03 - Unwrap beets and let them cool until manageable. Peel and cut into wedges or bite-size cubes.
04 - Whisk olive oil, balsamic vinegar, Dijon mustard, honey, salt, and pepper in a small bowl until emulsified.
05 - In a large bowl, toss arugula, roasted beets, and sliced onion with the dressing until evenly coated.
06 - Transfer the salad to a serving platter and scatter crumbled feta and toasted walnuts on top.
07 - Serve the salad immediately.