To make the gochujang sauce, mix the ingredients together in a small bowl and whisk until smooth.
In a large wok, heat 1 tablespoon of the oil. Stir-fry the onion, garlic and ginger until softened, about 2 minutes. Slice the zucchini into batons, julienne the carrots and thickly slice the cabbage.
Add another tablespoon of the oil to the pan and then add the zucchini, carrot and cabbage. Keep stir-frying until the vegetables are slightly softened. Pour in the sauce and add the kale, cut into chunks, and stir-fry for 2 more minutes. It should be hot and the sauce sticky on the vegetables.
Sprinkle the vegetables with the spring onion and sesame seeds. Serve with rice.