In a large bowl add in your red lentils and rinse with water and drain. Do this a couple of times until the water runs clear then top off with some more water until the lentils are fully submerged. Set aside and let the lentils soak until you need them.
In a large shallow pot add in the vegetable oil and heat it up on high. In a mortar and pestle slightly crush the coriander seeds - enough to open them up but not enough to make it into a powder. Add in the diced onion and crushed coriander seeds into the oil. Let the onions cook until they are golden brown and coriander is fragrant. This will take about 5 minutes.
Add in the diced tomatoes, spices, salt, garlic, and ginger. Mix everything together and then add in the drained red lentils. Top with 1½ cups water and mix. Cover and cook on a medium heat for 15-20 minutes until lentils are almost fully cooked.
Add in the peeled and cubed potatoes. Top with an additional ½ cup water to help potatoes cook. Bring everything to a simmer, cover with a lid, and cook for 20 minutes or until potatoes and lentils are soft. Stir occasionally to cook things evenly.
Now you can add in the cooked and drained chickpeas. Mix them in the salaan and let them pick up the flavors on a low heat. Let the chickpeas heat up for at least 10 minutes or longer.
Garnish with cilantro and serve up the cholay ka saalan immediately with some puri or parathay. They can also be used in a chaat.