In a small jar, combine olive oil, balsamic vinegar, minced garlic, and Dijon mustard. Add a pinch of salt and pepper. Shake vigorously for about 30 seconds until well-emulsified, then set aside.

Bring a large pot of salted water to a rapid boil. Add orzo and cook for 7 to 9 minutes, or until al dente, stirring occasionally. Drain and rinse under cold water to halt cooking, then let cool.

Soak sun-dried tomatoes in hot water for about 5 minutes to soften, then drain and pat dry.

In a mixing bowl, layer spinach, cooled orzo, and soaked sun-dried tomatoes. Crumble feta cheese on top and toss gently.

Drizzle balsamic dressing over the salad and toss gently until well coated.

Let the salad sit for about 15 minutes before serving to allow flavors to meld.