Lightly coat inside of slow cooker with canola oil to minimize sticking.
Cut flank steak into bite-sized pieces. Place steak into a plastic baggy and add corn starch. Seal bag and shake to coat. Alternatively, add the steak pieces in a bowl and coat steak pieces by shaking corn starch on top and flipping the steak pieces to coat. (Note: The corn starch might "disappear" when you leave steak pieces out for a few minutes while whisking together next ingredients; this is okay.)
In a small mixing bowl, whisk together low-sodium soy sauce, minced garlic, Truvia brown sugar blend and water.
Add steak and sauce mixture to slow cooker. Stir to cover steak with sauce.
Cook on high for 2 to 3 hours or on low for 4 to 5 hours or once internal temperature reaches at least 145°F (rare) or 160°F (medium).
Remove steak and sauce from slow cooker. Garnish with chopped green onion and serve over "cauliflower rice" or brown rice.