There are a couple of different reasons why a substitute for onions may be desirable. Perhaps there are people in the household who are allergic to onions. Maybe there are simply no onions in the house and there is no time or desire to run out and purchase a bag of onions. In either situation, there are some quick and easy ways to use other ingredients instead of onions and still have a tasty dish.
If the need for an onion substitute arises due to the fact there are no onions in the house, there are several options open. First, there is the possibility of substituting with a clove or two of garlic. The taste will be very close and the texture of minced garlic is very similar to that of finely chopped onion.
When no garlic is available, look in the spice rack. There is a good chance that you will find onion powder or onion flakes among the spices. Both options are a great substitute for onions. As a bonus, there is no chopping or dicing involved. Many cooks use the dehydrated onion flakes in soups, stews, and in meatloaf because they add a taste of onion without the mess.
For situations where allergies need to be considered, there are a couple of options that may work. One common substitute for onions is a nice bunch of leeks. Leeks have a milder taste than onions and are far less acidic. Many people who cannot eat onions can consume leeks with no problem. You can use the green tops as well as the white bulbs for a little added color to the dish.
When leeks are still a problem, you may want to look into such options as fried cumin seeds and perhaps asafetida, better known as hing. Both will add flavor to many recipes and are very friendly to constitutions that cannot handle onions for some reason. Hot peppers may also serve as a viable substitute for onions as well. Mince the peppers so the taste will be evenly distributed throughout the prepared recipe.