Cook pasta in salted water according to box instructions.
Drain cooked pasta and let it cool until no longer scalding hot.
Dice celery and green onion and herbs while pasta is cooling. Combine all ingredients for the dressing in a blender or food processor and blend.
Once pasta is cooled to room temperature, mix in celery and green onion (and other veggies if using) and refrigerate for a couple of hours, or overnight. Store the dressing in a separate container, in the refrigerator.
It's best to serve this macaroni salad cold and to mix the dressing right before serving.
When ready to serve, mix the salad with the dressing until evenly coated.