Peel the radish and cut into 2 1/2-inch sections; cut each section first into very thin slices, and then into fine slivers; combine with 3/4 teaspoon salt, then set aside for 15 minutes.
Discard the stems and seeds of the chili, and cut into fine slivers to match the radish; cut the scallion greens into similar slivers.
Drain the radish slivers and squeeze dry; set aside.
Mix the cornstarch and water into a paste.
Heat the wok over a high flame until smoke rises, then add the peanut oil and swirl around. Add the chili and sizzle for a few seconds before adding the radish slivers. Stir-fry vigorously for a couple minutes, adding the soy sauce and salt to taste, if necessary.
When the radish slivers are hot, add the scallions and vinegar and stir well to combine. Add the cornstarch paste to the middle of the wok, stirring rapidly as it thickens to a gloss. Finally, remove the wok from the heat, stir in the sesame oil, and serve.