Make the dressing: In a small jar, combine the olive oil, balsamic vinegar, honey, a pinch of salt, and black pepper. Shake well until combined.
Toast the nuts: Lightly toast the pistachios in a dry skillet over medium heat for 2 minutes until fragrant. Let them cool completely.
Assemble the base: Place the completely dried mixed greens into a large, wide serving bowl.
Add toppings: Scatter the fresh blueberries, sliced red onions, and crumbled feta cheese evenly over the greens.
Finish and serve: Sprinkle the cooled pistachios on top, drizzle with the prepared dressing, and gently toss just before serving.
