Preheat the oven to 200°C (400°F). Rinse the beets thoroughly under cold water to remove any dirt and trim off the stems and root ends if still attached. Leave the skins on, as they protect the flesh during roasting and help retain moisture. Pat the beets dry with a kitchen towel before wrapping.

Wrap each beet individually in aluminum foil and place them on a baking sheet. Roasting the beets individually helps them cook evenly and prevents their juices from burning on the tray. Roast for 40–45 minutes, depending on size, until a knife slides easily into the center of each beet. Once cooked, remove them from the oven and allow them to cool until they are comfortable to handle.

Once the beets have cooled slightly, gently rub the skins off using your fingers or a paper towel. The skins should slide off easily after roasting. Cut the peeled beets into bite-sized wedges or chunks, roughly 2–3 cm in size, so they distribute evenly throughout the salad.

Using a sharp knife, remove the top and bottom of the orange and grapefruit to create flat surfaces. Stand each fruit upright and carefully cut away the peel and white pith following the curve of the fruit. Hold the fruit over a bowl and slice between the membranes to release the citrus segments. This technique, known as supreming, produces clean, membrane-free segments. Collect any juice that drips into the bowl and reserve 1 tablespoon for the dressing.

Rinse the arugula thoroughly under cold water and dry it completely using a salad spinner or clean kitchen towel. Dry greens are essential so the dressing adheres evenly rather than sliding off.

Place the walnuts in a small dry skillet over medium heat and toast for 2–3 minutes, stirring occasionally, until they become fragrant and lightly browned. Remove them from the pan immediately to prevent burning and allow them to cool before adding to the salad.

In a small bowl combine the reserved citrus juice, white wine vinegar, extra virgin olive oil, Dijon mustard, sea salt, and black pepper. Whisk vigorously for 15–20 seconds until the dressing emulsifies and becomes smooth. The vinaigrette should taste balanced between acidity, brightness, and gentle richness from the olive oil.

Spread the arugula evenly across a large serving platter or shallow bowl to create the base of the salad. Distribute the roasted beet wedges evenly across the greens so the earthy sweetness of the beets contrasts with the peppery arugula.

Arrange the citrus segments evenly over the salad, allowing the bright orange and grapefruit pieces to add color and freshness. Sprinkle the toasted walnuts across the salad for crunch, then scatter the torn mint leaves for aromatic freshness.

Drizzle the citrus vinaigrette lightly over the entire salad just before serving. Serve immediately so the arugula stays crisp and the citrus remains juicy and fresh.