Heat a wok or large skillet over high heat. Add 2 tablespoons of the oil and heat for 30 seconds. Add the steak and stir-fry until cooked through, 3 to 4 minutes. Transfer to a plate. Wipe out the pan. Reduce heat to medium-high, add the remaining oil, and heat for 30 seconds. Add the bell pepper and cook, stirring constantly, for 10 seconds. Add the sweet potato and water. Cover partially and cook, stirring occasionally, for 7 minutes. Add the peas and scallions and cook for 1 minute. Add the Garlicky Hoisin Sauce and increase heat to high. When it starts to bubble, add the steak. Stir-fry until warmed through, about 1 minute. Serve immediately over the rice.
Tip: Pork or turkey cutlets can stand in for the beef, and green beans for the sugar snaps.