In a medium bowl, whisk together olive oil, balsamic vinegar, Dijon mustard, minced garlic, salt, and pepper until well combined.

Bring a large pot of salted water to a rolling boil. Add orzo and cook according to package instructions, about 7-9 minutes, until al dente. Drain and rinse with cold water.

In a small bowl, soak sun-dried tomatoes in hot water for about 5 minutes, then drain and press to remove excess moisture.

In a large mixing bowl, combine spinach, cooked orzo, soaked sun-dried tomatoes, and crumbled feta cheese. Gently toss to combine.

Drizzle the vinaigrette over the salad mixture, toss gently, and adjust seasoning to taste.

Serve the salad at room temperature or chill in the fridge for up to an hour before serving.