In general, shallots, leeks, or chives would be milder than regular onions and probably a closer approximation to green onions, though all are usually harder to find than green onions. Leeks and chives have the advantage that they also have a similar color to green onions. read more
I think chives would be the closest in taste and texture. Leeks are also pretty close in flavor but, again, not exactly the same. read more
We don't miss the flavor, but I can't help but think that the recipe step of sautéing onions is important. (Giving spices a chance to release their flavors into the oil/butter/etc.) I've tried substituting celery, apples, and even finely chopped collard green stems, but those textures don't fade away like an onion can melt into the background. read more