Add sliced flank steak and cornstarch to a large resealable plastic bag. Close and shake to coat steak in cornstarch; transfer to the slow cooker.
In a medium bowl, whisk together the oil, garlic, ginger, water, soy sauce, brown sugar, and Sriracha. Pour over the steak and gently mix to coat steak. Top with carrots and cover slow cooker with the lid.
Cook on low for 5-6 hours, until steak is cooked and tender.
Serve over rice and garnished with sesame seeds, if desired.