Separate the Chinese broccoli leaves, along with the tender stems, from the stalks. Cut the leaves and stems crosswise about 2 inches long. Cut the stalks on a sharp diagonal (about 30° angle) into 2-inch sticks. (If using the crowns of regular broccoli, cut them into bite-size florets.) Empty the can of fried dace into a bowl; use a small rubber spatula to scrape every bit of the flavorful oil into the bowl. Use two forks to shred the fish meat into small pieces, about the size of a mini Tootsie Roll. Heat a wok or a 12-inch skillet on high heat. When hot, add the oil, garlic, and chiles; stir constantly until fragrant-you should be sneezing a little-then add the broccoli. Stir-fry until the broccoli wilts just so slightly, less than a minute. Add the fish along with the black beans and every drop of the oil; stir until everything is warmed through with the broccoli still bright green, tender-crisp, and thoroughly interspersed with the fish bits and the black beans, about 1 minute. Immediately transfer to a plate and serve with plain jasmine rice.