Heat the vegetable oil in a large saute pan or pot or Dutch oven. Add the onions with half a teaspoon each of salt and pepper. Saute, stirring frequently, until the onions are golden-brown and well-caramelized. This is really important for your dhansak to get that characteristic brown color and deep flavor.
Add the ginger garlic paste and saute a few more seconds.
Add the cooked lentils and vegetables to the pot with three cups of water. Mix well.
Turn off heat and use an immersion blender to blend the lentils and veggies. I like leaving in a little bit of texture, as is done traditionally, but you can blend to a smooth puree, if you wish. You can also do this by transfering the lentils and veggies to a blender. Be careful when you blend hot liquids and exercise all necessary precautions. If you can't do either, use a potato masher to thoroughly mash the veggies and lentils.
Bring the dal to a boil, then stir in the dhansak masala mix you just prepared. Add salt to taste. For more color you can stir in a teaspoon of paprika, if you like. You can add more water if the dal is too thick--I use 4-5 cups in all. Remember, it should be thick but pourable and definitely not soupy.
Cover the dhansak and cook for 30-45 minutes, stirring frequently to ensure it doesn't stick, until the dal looks glossy. Check seasoning at this time and add more salt if needed.
Garnish with remaining cilantro and serve hot.