Wash the mixed salad greens thoroughly under cold water and dry completely.

Rinse the fresh blueberries and drain. Chop the shelled pistachios into smaller pieces.

In a large salad bowl, toss together dried mixed greens, blueberries, and chopped pistachios. Add crumbled feta cheese and sliced red onion.

Whisk together olive oil, honey, balsamic vinegar, Dijon mustard, salt, and pepper until well combined.

Pour the dressing over the salad and gently toss to combine without crushing the blueberries.

Taste and adjust seasoning with more salt or pepper if necessary.

Serve immediately or chill in the refrigerator for 15 minutes before serving.