Start by slicing the red onions and placing them in a bowl.
Top the onions with the sumac, olive oil, salt, chopped coriander leaves, lemon juice and chili flakes.
Mix everything together well and refrigerate for an hour.
Serve with your favorite Middle Eastern foods, or just as a side salad.
Notes
Some varieties of onions tend to have a very strong, pungent taste and aroma. To tackle this, you can transfer the sliced onions to a bowl and refrigerate for 30 minutes. If your eyes tend to water while cutting onions, you may want to first peel them, soak them in water for 15-30 minutes and then slice and use them to make Sumac onions. Apple cider vinegar can be a wonderful alternative to lemon juice for this recipe. It lends the salad that nice sourness you’re looking for, and is super healthy too. If you want to make these marinated onions a bit spicy, you can also add a dash of paprika or some cayenne pepper into it. To tone down the sourness of the Sumac onions, add a bit of sugar into the mix. To get the perfect thin slices, use a mandolin slicer.