Whisk the first three ingredients together in a small mixing bowl. Gradually whisk in olive oil to form an emulsion. Season with salt and pepper. Set aside.
Bring chicken stock to a boil in a large pot. Add orzo, stir and reduce heat to medium. Cook per package instructions, about 7-10 minutes, until al dente. Drain and transfer to a serving bowl. Immediately add dressing and toss.
Add tomatoes, basil, green onions, feta and pine nuts. Or make it a complete meal by adding shredded chicken and chopped grilled vegetables. Toss again. Serve at room temperature.