Cut the flank steak into thin strips and coat them with corn starch.
Brown the steak in a skillet with olive oil and set aside.
Mix garlic, soy sauce, water, and brown sugar in a bowl.
Transfer the steak to a slow cooker, pour the sauce over it, and cook on low heat for 6 hours.
Add onions, green peppers, and red peppers to the slow cooker after 4 ½ hours.
Continue cooking for an additional 1 ½ hours until vegetables are tender.
Serve over rice, noodles, veggies, or quinoa.
