Peel the radishes. Thinly slice them and the sweet potato in roundels. Soak them in water for some time. Chop spring onions and add to the same bowl of water. Heat vegetable oil in a pan. Saute chopped spring onion ginger, garlic, and red chillies. Add drained vegetables. Season with salt. Add soy sauce, water, and sugar. Toss the vegetable mix. Add some chopped coriander leaves. Cook for 5 to 6 minutes on a low flame. Serve sweet potato and radish with soy glaze by garnishing with spring onion greens and some mint leaves.