Wash and cut the Kovakkai into 4 to 5 thin pieces lengthwise. Add turmeric powder and salt and mix well. Keep it aside.
Chop onion finely.
In a kadai put the oil and add mustard. When it pops up, add urad dhal, jeera and curry leaves. Fry till the dhal turns light brown. Then add chopped onion and fry till it is transparent. Now take the kovakkai pieces and squeeze out the extra water content and add to the fried onions. Fry it for few seconds. Add sambar powder and mix well. If necessary sprinkle a handful of water and mix well. Close with lid and cook on medium flame. Stir now and then and keep it on stove till it is soft. Before removing sprinkle the pepper powder and stir fry for few more seconds and remove.