Heat wok over high heat until you see wisps of smoke. Add 1 tablespoon peanut or canola oil, turn down heat, and add yacai. Stir-fry briefly, just to warm through. Remove and set aside.
Wash out wok and return to high heat. When wok is hot, heat 4 tablespoons oil and swirl it up the sides of the wok. Lower heat and add eggs. Swirl eggs just a bit up the wok, then leave to sit and cook undisturbed until they are about 3/4 done. The longer you leave the omelet to cook undisturbed, the larger the egg pieces in the final dish. Be careful not to brown them.
Add rice, yacai and scallions (leaving a few out for garnish) and stir-fry with the egg, mixing well and breaking up any clumps of rice (there won't be many since you're using freshly cooked rice). Turn up heat to high and let wok sit on heat to sear a few rice grains, then continue to stir-fry. Do this a couple times. Add the soy sauce to the chicken broth and drizzle the mixture around the edges of the wok. Stir-fry until well mixed and very hot, being careful not to break down all the egg bits.
Plate and garnish with remaining scallions.