Choose a substitute that matches your goal: crisp stems (gai lan, broccoli rabe) or tender leaves (napa cabbage, spinach).
Use the listed ratio; if your substitute is leaf-only (spinach), add it at the end instead of early in the stir-fry.
Adjust timing: sauté stem-heavy options 1-2 minutes before adding leaves; add fast-wilting greens only for the last 30-60 seconds.
Balance flavor: if the swap is bitter (broccoli rabe), slightly increase the sauce’s sweet element (or reduce acidic notes).
Finish the texture: stop cooking as soon as greens are just tender to avoid mushy results.