In the basin of a 4- to 6-quart slow cooker, whisk together the coconut aminos, sweetener, rice vinegar, smashed garlic, grated ginger, and crushed red pepper flakes.
Arrange the short ribs in a single layer in the sauce.
Place the cabbage quarters on top of the ribs.
Cover and cook on low for 7 to 8 hours, or on high for 4 to 5 hours, until the meat is exceptionally tender and pulls easily from the bone.
Carefully transfer the cooked short ribs and cabbage to a serving platter. Tent with foil to keep warm.
Using a large spoon, skim the excess fat from the surface of the cooking liquid in the slow cooker and discard.
Turn the slow cooker setting to high.
In a small bowl, create a slurry by whisking the guar gum with 1 tablespoon (15 ml / 0.5 fl oz) of water until completely smooth.
Whisk the slurry into the cooking liquid.
Continue to cook on high, stirring occasionally, until the sauce has thickened, about 2 to 3 minutes.
Stir in the toasted sesame oil.
Spoon the thickened sauce generously over the short ribs and cabbage.
Garnish with thinly sliced scallions before serving.
