Cook orzo pasta according to package instructions. Drain and set aside to cool.
Preheat grill or stovetop grill pan over medium-high heat. Season beef sirloin with salt and pepper. Grill for 3-4 minutes per side, or until cooked to your liking. Remove from heat and let rest for a few minutes before slicing into thin strips.
In a large mixing bowl, combine cooked orzo pasta, grilled beef, cherry tomatoes, cucumber, red onion, feta cheese, and fresh herbs.
In a small bowl, whisk together olive oil, red wine vinegar, Dijon mustard, garlic, salt, and pepper to make the dressing.
Pour the dressing over the salad and toss to combine. Season with additional salt and pepper, if needed.
Serve the Orzo Beef Salad immediately, or refrigerate for later. Enjoy!