Combine orzo, cucumber, green onions, and tomatoes in a large bowl. Place dill, vinegar, and mustard in a blender and blend until smooth. With the motor running, slowly add the olive oil and blend until emulsified. Season with salt and pepper, to taste. Pour the vinaigrette over the orzo mixture and stir well to combine. Gently fold in the feta cheese.
Heat grill to high. Brush shrimp with oil and season with salt and pepper. Grill for approximately 2 minutes per side or until just cooked through. Divide orzo salad among 4 take-out containers or plates and top with 4 shrimp. Garnish with additional dill.