Place the baby arugula in a large bowl of cold water and gently move the leaves around with your hands to loosen any dirt or grit. Lift the leaves out of the water rather than draining them through a colander so sediment remains at the bottom of the bowl. Transfer the arugula to a salad spinner and spin until completely dry. If a spinner is unavailable, pat the leaves dry carefully with clean kitchen towels. Thoroughly drying the greens is important because excess moisture prevents the dressing from coating the leaves properly and dilutes the flavor of the salad. Once dry, transfer the arugula to a large mixing bowl and refrigerate briefly while preparing the remaining ingredients.

Using a sharp knife, cut the top and bottom off each orange and the grapefruit so the fruit can stand flat on the cutting board. Slice downward along the sides to remove the peel and white pith completely, following the natural curve of the fruit. Once the citrus flesh is fully exposed, carefully slice between each membrane to release clean citrus segments. Allow the segments to fall into a bowl and gently squeeze the remaining membranes to collect any extra juice. Reserve about 30 ml of this fresh juice to use in the dressing.

If the almonds are not already toasted, place them in a small dry skillet set over medium heat. Toast for 3–4 minutes, stirring frequently, until the almonds become lightly golden and fragrant. Transfer them immediately to a plate to cool so they do not continue cooking in the hot pan. Toasting enhances the nutty flavor and adds a crisp texture that contrasts with the tender greens and juicy citrus.

In a small bowl combine the fresh orange juice, lemon juice, olive oil, honey, Dijon mustard, salt, and black pepper. Whisk the mixture vigorously for about 20 seconds until it becomes lightly emulsified. The mustard helps stabilize the emulsion while the honey balances the natural acidity of the citrus juices. Taste the dressing and adjust seasoning if necessary, adding a pinch more salt or lemon juice to achieve a bright and balanced flavor.

Remove the chilled arugula from the refrigerator and drizzle about two-thirds of the vinaigrette over the leaves. Using salad tongs or clean hands, gently toss the greens until they are lightly coated. Because arugula is delicate, mix gently to avoid bruising the leaves.

Carefully add the orange and grapefruit segments to the bowl with the dressed arugula. Toss very gently to distribute the fruit without breaking the segments. The citrus should remain intact so it releases juice gradually as the salad is eaten.

Divide the dressed arugula and citrus mixture evenly among four serving plates. Arrange the citrus segments so they are visible on top of the greens for an attractive presentation.

Sprinkle the toasted almonds evenly over each serving, then add the shaved Parmesan cheese. The almonds provide crunch while the Parmesan contributes savory depth that balances the sweetness of the fruit.

Serve the salad immediately after assembling. Arugula wilts quickly once dressed, so the best texture and flavor occur when the salad is enjoyed right away.