Wash the chana dal with water 2-3 times till the water starts running clear. Transfer to a bowl and add enough water to fully submerge the chana dal. Soak it for 1 hour 30 minutes, and no longer than that. Once soaked, drain all of the water. Remember to drain as much as possible as excess water will lead to a soggy mix.
Add all the ingredients mentioned under 'dry masala' in the chutney jar of the mixer. Grind till it becomes a coarse powder. Transfer the masala mix to a bowl and keep aside.
Add half of the soaked and drained chana dal to the same chutney jar. There is no need to clean the jar. Grind till is becomes a coarse mix, do not grind too much as it will become too loose to make vadas. Its okay if you see a few pieces of whole chana dal. Remove the first batch and transfer to the mixing bowl and repeat the same with the remaining half of the chana dal. Once done, transfer to the mixing bowl.
Add mint, curry leaves, onions, green chilli, ginger garlic paste, turmeric powder, salt and the dry masala to the mixing bowl. Use your hands to mix and make sure it is well combined. Shape them into golf ball sized round balls and then flatten them using your palms to make a vada. Remember to tightly shape them so they do not fall apart while frying. Keep aside.
Use a kadai or a heavy bottomed pan for frying. Pour in about 1.5 inches of oil and allow it to heat up. Add a small piece of the vada mixture to the pan to check if the oil is hot enough. The vada should float to the top; if it sinks that means the oil is not hot enough. If it browns too quickly, it means the oil is too hot. The vada needs to cook on a low flame so the inside gets cooked evenly without the outside browning too much too soon.
Once the oil is hot, add as many vadas as possible in a single layer. Do not move or turn the vada for 2-3 minutes after adding as they tend to disintegrate. Do not crowd the pan, fry only a few at a time.
Fry the vadas for 10-12 minutes on a low flame. Use a skimmer to turn them halfway through so they brown evenly on both sides. Remove from pan and place over a kitchen tissue or in a colander to drain the excess oil. Serve hot.