As we know that there are people going vegetarian for various different reason. Some vegetarian just don't eat meat, fish and other marine products. But some even don't eat onion, garlic, leeks and food of those kinds. These foods are said to have harm to people who don't eat meat at all (even though we usually hear that those foods have health quality, improving health in certain aspect).
I ever bought vegetarian Tah-mee (a kind of Chinese thin noodles with tomato sauce). This word "Tah-mee" is a word of Teochew, one of Chinese dialect. "Tah" means "dry" (cause it's dry tomato sauced). And "Mee" means "noodles".
"Tah Mee" usually has fried onion on it. Is it real fried onion or just some kind of food that is made to look like fried onion? Well, in fact the fried onion in the Tah-mee is not real one. Vegetarian restaurants know that some people don't eat fried onion so they put vegetarian fried onion which is "fried cabbage" which is cut into small pieces and fry until the color looks like real onion. And this is one of the simple secret in vegetarian food. Of course they don't smell like real onion. Just for the look in that Tah-mee.