How to Make It
Trim leafy greens from bok choy; chop greens and reserve. (You should have about 2 cups.) Cut stalks into 1-inch pieces. Discard root ends.
Heat a large cast-iron skillet or wok over high heat. Add oil; swirl to coat. Add bok choy stalks and onions. Stir-fry until just softened, about 2 minutes. Add reserved greens, soy sauce, sugar and chili. Stir-fry until liquid has thickened, about 1 minute. Transfer mixture and sauce to a serving bowl. Top with cashews, radish slices and sesame seeds; serve immediately.