How to retain the smell of frying green onions/scallions in cooked dish? I have always loved the smell of frying green onions/scallions but was never able to retain the smell of it when the dish is done cooking. 

I was in Singapore about 1.5 years ago and in a small food court, I enjoyed a plate of fried rice noodles and the aroma of the frying scallions was very much present which made the dish much better. 

I was not able to replicate it at home, no matter when I put the scallions in, the aroma always disappeared at the end. The smell of it was quite strong in the dish I had and I have no idea how it is done. 

Is there a trick to retain the smell of frying scallions? or maybe it's something else that producing the smell?
You were probably having a dish with green onion oil, something I'd also recommend as a solution to the smell/taste you're looking for.  It remains aromatic for a couple weeks after you make a batch and bottle it. I make one with darker brown onions like this, which allows me to store it even longer.