Preheat the oven to 170°C/ 325°F/ gas mark 3. Prepare your baking rack.
Trim away all fat from flank steak or ask your butcher to do this for you.
Place the steak in a freezer bag and chill in the freezer until firm but not completely frozen about 2 hours.
While the meat is freezing you can make the coating. In a medium bowl, combine the soy sauce, cumin, chilli powder and garlic.
When the meat is ready, remove from the freezer and place on a flat surface.
Slice into 1/2 inch wide strips.
Place the slices into the soy sauce mix and toss to coat. Leave to soak for about 10 minutes.
Remove from the bowl and leave to air dry on a baking rack for about 3 hours.
Place in the oven on the wire racks for about 4 hours.
Leave to air dry overnight before serving.