1. In a large skillet, heat the vegetable oil over medium-high heat.
2. Add the beef cubes to the skillet and sear them on all sides until browned, about 3-4 minutes.
3. Transfer the seared beef to the slow cooker.
4. In a small bowl, whisk together the soy sauce, beef broth, brown sugar, minced garlic, and black pepper.
5. Pour the soy sauce mixture over the beef in the slow cooker.
6. Cover and cook on low for 6-7 hours or on high for 3-4 hours, until the beef is tender.
7. In a small bowl, mix the cornstarch with water to create a slurry.
8. About 30 minutes before serving, stir the cornstarch slurry into the slow cooker to thicken the sauce.
9. Serve the steak bites hot, garnished with chopped green onions if desired.
Variations & Tips

For a spicier version, add a teaspoon of red pepper flakes or a dash of hot sauce to the soy sauce mixture. You can also experiment with adding different vegetables to the slow cooker, such as sliced bell peppers or mushrooms, to create a more robust dish. If you prefer a sweeter flavor, increase the amount of brown sugar or add a tablespoon of honey. For a gluten-free version, ensure you use a gluten-free soy sauce. Finally, if you want a richer sauce, substitute some of the beef broth with red wine.