Choose your target use: raw crunch (salads, slaws) vs. cooked crunch (stir-fry or warm sides).
Pick the substitute with the closest texture: cucumber/radish for raw, water chestnuts for cooked, chayote/apple for mild flavor.
Cut into similar sizes (matchsticks or thin slices) so the bite feels like jicama.
If your swap releases extra liquid (cucumber or canned water chestnuts), peel and pat dry (or drain and rinse) before using.
Season to mimic jicama: add lime/lemon and a small pinch of salt; for sweeter profiles, lightly add sugar or honey only if needed.