Cut flank steak into thin strips. In a ziplock bag add flank steak pieces and cornstarch. Shake to coat.
Add olive oil, minced garlic, soy sauce, water, and brown sugar to slow cooker. Stir ingredients. Add coated flank steak and stir again until coated in the sauce.
Cook for high 2-3 hours or on low 4-5 hours until cooked throughout and tender. Serve with Stir Fry Veggies.