Heat sesame oil in a large skillet over medium high heat. Quickly sear flank steak for a few seconds, then transfer to a crock cooker. Add onion and broccoli on top of steak.
In a medium bowl, whisk together next 6 ingredients (garlic through coconut aminos). Pour all over beef and veggies, give it a good stir, then cook on LOW for 4 to 6 hours or HIGH for 3 to 4 hours. The steak should be fork tender. Remove half the beef and broccoli and then set aside for lunch the next day.