Soak 1 cup chana dal in water for ~3 hours. There should be enough water to completely submerge the dal. Drain the water after that time period, making sure not to leave behind a lot of water! It’s important not to over-soak the dal, as it will then absorb a lot of oil when it is fried.
Add 1 Thai chili, 1 inch ginger and 4 garlic cloves to a food processor and grind until it forms a fine mince. Scrape the sides of the food processor if needed to help move the ingredients back to the center.
Add the soaked and drained chana dal, ½ bunch cilantro, ½ teaspoon cinnamon powder, ½ teaspoon cumin powder, and 1 teaspoon fine sea salt into the food processor. Pulse the ingredients until it forms a medium coarse texture (you don't want to form a paste).Test the mixture by taking a small handful and squeezing it in the palm of your hands and then place it on a sheet tray. It should be able to hold its shape without falling apart. If it continues to fall apart, grind it longer. If you over-grind the chana dal to a paste it will result in a denser masala vada. If you under-grind the mixture it will fall apart in the oil.
Empty the mixture into a large bowl. Add diced onions, 25-30 curry leaves, and 3 tablespoons besan or chickpea flour and mix with a spatula. The reason we add the onions and curry leaves at this stage is to ensure that the food processor doesn’t blitz these ingredients too finely!
Take about 2 tablespoons of the mixture in the palm of your hands. Take your time and use pressure to flatten and form a ½ inch disc for the vadas. If you are a beginner, it helps to form smaller vadas that are ~1 tablespoon each. Set the formed vadas on a sheet tray until ready to fry.
Heat a deep and wide heavy-bottomed pot with ~2 inches of vegetable oil to 325 F. Set up a sheet tray with a wire rack next to the oil to transfer the cooked vadas.
Gently add the vadas in a single layer in the pot and do not touch them for at least 1 minute or until the vadas have formed a bit of a crust. Fry on each side for ~2 minutes or until the vadas are golden brown on both sides. Frying on a lower heat ensures that the chickpeas have enough time to cook all the way through before the outside gets brown.
Remove the vadas with a slotted spoon and place on a wire rack. Sprinkle with salt while still warm. Enjoy immediately as an appetizer or as a crunchy side dish.