Wash the vendakkai well and wipe them completely dry using a clean cloth. Trim the ends and cut into ½-inch pieces. Ensure there is no moisture to avoid stickiness.
Heat 1 tablespoon oil in a pan. Add the chopped vendakkai and fry on medium flame, stirring occasionally, until the sticky texture disappears and the pieces look lightly roasted.
Remove the roasted vendakkai from the pan and keep aside.
In the same pan, add 1 teaspoon oil. Add mustard seeds and allow them to splutter.
Add curry leaves and saute for a few seconds until aromatic.
Add the roasted vendakkai and back into the pan with sliced onion. Add red chilli powder, coriander powder, turmeric powder, and salt.
Mix everything well so the spices coat the vendakkai evenly. Close the pan with a lid and cook on low flame for about 5 minutes. This allows the vendakkai to cook fully and absorb the spice flavours without burning.
After 5 minutes, open the lid and gently stir. Continue sautéing on low to medium flame, stirring occasionally, until all moisture evaporates and the vendakkai becomes completely dry and crisp. This step may take a few more minutes, so be patient and avoid high flame.
Once the vendakkai is well cooked, dry, and nicely crisp, switch off the flame and serve hot.