Warm oil inn a saute pan. Add the urad dal if using, allow to develop a little golden color. Then add mustard seeds, cumin seeds, curry leaves, chilli pepper, and hing.
Allow all the spices to sizzle for a few seconds until toasty. Now add the chopped okra and saute on high heat for 2-3 minutes. Cover and cook for another 3-4 minutes on medium heat.
Stir so the okra cooks evenly. Once the okra is tender, but still has its bright green color. Add salt and toss well. Take it off the heat and allow to cool for about 15-30 minutes, just enough for the okra feels its at room temperature not hot.
Add the chopped onion and whisk yogurt and mix well. Taste and season if needed. Cool and refrigerate before serving.