1. Heat vegetable oil in a very large, high-sided skillet or wok over high heat. Sauté the mushrooms, stirring, for 1 minute.
2. Add the onion and garlic and continue cooking, stirring constantly, until garlic is slightly softened, about 5 minutes. Add the pork and broccoli; cook, stirring constantly, until the pork begins to brown, about 5 minutes.
3. Add the water chestnuts, broth, and sesame oil; cook for 2 minutes. Garnish with sesame seeds. Serve on its own or with rice, rice noodles, or quinoa.
To make ahead, slice the pork tenderloin into medallions and then into thin strips; place in freezer bag and freeze for up to a month.