Whisk the soy sauce, apple cider vinegar, dark soy sauce and brown sugar together. In a separate small bowl, mix the corn starch with water.
Heat cooking oil in a wok over medium high heat. Add the lotus root slices and stir-fry until slightly coloured before adding garlic and chili and stir-fry further until aromatic.
Add the sauce, and toss to coat the lotus root slices.
Drizzle the corn starch into the mixture until the sauce thickens. This will happen very quickly. Give it a quick stir, then turn off the heat.
Transfer the dish to a serving plate and garnish with spring onions.