Cook orzo according to package directions. Rinse with cold water and set aside.
Make the dressing in a small bowl by whisking together lime juice, olive oil, onion powder, garlic powder, and salt. Stir in cilantro and pour over cooked orzo.
Toss pasta with green onions, bell pepper, and tomatoes. Season with salt and pepper to taste. Refrigerate until chilled and/or ready to serve.