Slice or cut the flank steak into even 1/2 inch wide strips. Add the steak strips to a medium mixing bowl. Sprinkle the xanthan gum evenly over the steak pieces. Use your hands to toss the beef and gum together, lightly coating the steak strips all over in the powder.
Heat the olive oil in a large skillet over a medium heat. Add the coated beef strips. Pan-fry the beef for 4-5 minutes until well browned all over. Remove the beef from the skillet with a slotted spoon and set to one side while you prepare the sauce.
Finely crush the garlic and grate the ginger. Add the garlic and ginger to the skillet and sweat gently for a minute to soften. Add the tamari sauce, water and maple-flavored syrup. Stir together well to combine. Simmer the sauce for a minute until bubbling and beginning to thicken.
Return the steak strips to the skillet. Stir well to combine with the sauce. Pan-fry the beef for 2-3 minutes more until the sauce is reduced right down and thickened to a sweet sticky glaze, coating the beef all over. If the skillet gets too dry, you can always add a splash more water. This will help to deglaze the pan and lift any caramelized sauce from the base of the skillet. If your sauce is not thickening, you may also add a touch more xanthan gum as required.
Roughly chop the scallions. Divide the cooked beef between two individual serving bowls and top with the chopped scallions. Serve the Mongolian beef hot accompanied by your favorite Keto Chinese inspired sides.