Bring a large-pot of salted water to boil. Add the orzo & cook till al-dente, according to package instructions. Before draining, book roughly ½ cup pasta-cooking-water. Drain and rinse the orzo under cold running water till the orzo is no longer-warm. Drain well.
Toast the almonds in a medium-skillet over moderate heat, stirring regularly for 5minutes or till aromatic & turning golden on the edges. Transfer the almonds to a cutting-board and chop them.
In a large-serving-bowl, blend the cooked orzo, olives, raisins, chopped almonds, green-onion, parsley and feta (if using).
In a liquid measuring cup or small bowl, combine the orange-juice, orange-zest, vinegar, olive-oil, salt and garlic. Add ¼ cup of the reserved pasta-cooking-water and whisk till combined.
Pour the dressing on the salad and toss to blend. Season with pepper, to taste.
Season to taste with additional salt, if needed, and then serve. Leftovers will keep well in the fridge for up to 4-days.