Leek (Best Option)
1/2 cup chopped leek per 1/2 cup chopped onionLeeks belong to the same Allium family as onions and contain similar sulfur compounds that provide the characteristic onion flavor. Their mildness ensures they don't overpower the dish, and their structure allows them to soften without disintegrating under high heat.
When using leeks, clean thoroughly to remove grit and slice them thinly to ensure even cooking. Because they are milder, you might want to slightly increase the quantity if a stronger flavor is desired.
Compared to onions, leeks produce a subtler aroma and a slightly sweeter taste, which can enhance the stir-fry without changing its fundamental flavor profile.