Add the beef to a large skillet over medium-high heat. Cook the meat, stirring it to break up the pieces occasionally, until it is mostly brown, about 5 minutes.
While the beef cooks, chop the veggies and make the sauce. Add the tapioca or cornstarch to a measuring cup or bowl. Add a splash of the beef broth and mix. Add the rest of the broth and remaining sauce ingredients and mix again.
When the beef is mostly cooked, add the mushroom and cook them for 5 minutes. If there is more than 1 tablespoon of the oil in the pan remove it by tilting the pan to the side and using a spoon to scoop it out. If there is less, add a splash of oil.
Add the remaining veggies to the pan and cook for 5-6 minutes, or until they are crisp-tender.
Stir the sauce to mix up the starch then pour it into the pan. Once the sauce has thickened (1-2 minutes) serve the stir fry over rice or cauliflower rice.
Notes
Feel free to use your favorite veggies instead of the ones listed in the ingredients. You'll want to use about 8 cups of chopped vegetables.