Ginger Beef, Mushroom and Kale Stir-Fry

1/3 cup soy sauce (if making gluten-free, be sure to use GF soy sauce)
1/2 cup vegetable broth (or chicken/beef broth, or water)
3 tablespoons rice wine vinegar
2 tablespoons corn starch
2 teaspoons ground ginger
1/4 teaspoon freshly-ground black pepper
1 lb. thinly sliced flank steak or sirloin, cut diagonally across the grain into thin strips
2 garlic cloves, minced
2 tablespoons olive oil
8 ounces baby portobello or button mushrooms, halved
4 ounces shiitake mushrooms, halved
3 cups chopped kale
2 green onions, thinly sliced

Directions

1. Add all marinade ingredients to a bowl and whisk to combine. Pour marinade into a large bowl or ziplock bag, then add in the steak and gently toss to combine. Cover/seal and refrigerate for at least 15 minutes.
3. Once steak has marinated, heat 1 tablespoon oil in a large saute pan over medium-high heat. Remove steak from marinade with a slotted spoon, reserving the marinade, and add to saute pan with garlic. Saute for about 2-3 minutes until browned, stirring occasionally. Remove steak with a slotted spoon and set aside.
4. Add remaining tablespoon of oil to the pan. Then add in the mushrooms, kale, and reserved marinade, and stir to combine. Cook for 3-4 minutes, until the kale is wilted, the sauce has thickened and come to a boil, and the mushrooms have cooked, stirring regularly so that sauce does not burn. Add in the steak, and toss to combine.
5. Serve immediately over rice or quinoa, garnished with chopped green onions.