Cook the orzo in a large pot of salted water until al dente, according to package instructions. Drain, then transfer to a large mixing bowl.
While the orzo cooks, make the dressing: In a bowl or liquid measuring cup with a spout, whisk together the oil, vinegar, garlic, mustard, salt, oregano, and black pepper.
While the orzo is still warm, pour about half of the dressing over it and stir to coat (this helps the orzo absorb the dressing flavor and keeps it from sticking together).
To the bowl with the orzo, add the cucumber, tomatoes, bell pepper, chickpeas, feta, olives, and basil. Toss to combine, adding more dressing so that every is nicely moistened.
Taste and add more salt and pepper for additional seasoning or a splash or two of vinegar for more zing. Refrigerate until ready to serve; just before serving, toss with a bit more dressing.
Notes
TO STORE: Store leftovers in an airtight container in the refrigerator for up to 3 days. Give it a good stir before serving and add more dressing if needed.