To maximize flavor release when slicing green onions, use a sharp knife and slice them thinly on a bias (at an angle). This ruptures more cells, releasing more of their flavorful compounds.
Green onions contain flavor compounds stored within their cells. When you slice them, you break these cells open, releasing those compounds. The more cells you break, the more flavor you get. Slicing thinly increases the surface area exposed and the number of cells ruptured. Slicing on a bias (at an angle) further increases the cut surface area compared to slicing straight across. A sharp knife is crucial because a dull knife will crush the cells instead of cleanly slicing them, resulting in less flavor release and a bruised texture. Using a sharp knife ensures a clean cut, maximizing the release of allicin and other flavor-enhancing compounds.
Use the green parts of the onion immediately after slicing, as the released flavor compounds are volatile and can dissipate quickly. The white parts can be stored longer, but still benefit from being sliced just before use for optimal flavor.