Roast the Beets: Preheat your oven to 400°F (200°C). Wash and wrap each beet individually in aluminum foil, then place them on a baking sheet. Roast for 45–60 minutes until tender. Allow to cool.

Prepare the Oranges: Peel oranges and slice into 1/4-inch rounds, removing any white pith.

Chop the Fresh Mint: Finely chop fresh mint leaves.

Toast the Walnuts: In a dry skillet over medium heat, toast walnuts for 3–4 minutes until fragrant. Cool and chop coarsely.

Whisk the Dressing: In a mixing bowl, combine Dijon mustard, red wine vinegar, and orange juice. Gradually whisk in olive oil, season with salt and black pepper.

Assemble the Salad: In a large bowl, layer spinach or arugula, add roasted beets, and arrange orange slices.

Add the Finishing Touches: Sprinkle with mint, feta cheese, and walnuts.

Dress and Serve: Drizzle dressing over the salad, gently toss before serving.