@liuzhou -- you start a tarka with cumin seeds, whole garlic, fenugreek seeds and curry leaves. Add a chopped onion and saute until soft, then add ginger and chopped garlic. Finally, a pinch of turmeric, some coriander, and some chili powder. Stir the wilted spinach into this and saute for ten minutes for so.
Edited to add: it's pretty close to this recipe at Saveur.