Rinse the dal in a fine-mesh sieve under running water for 30 seconds, swishing it with your fingers to clean it thoroughly. Drain and transfer to a bowl, covering with plenty of warm water to soak while you prepare the aromatics.

Heat the oil in a saucepan over medium-high heat. Add the onion and cook until the edges begin to brown and caramelize, about 5 minutes.

Add the garlic, ginger, and green chili to the pan and cook for 1 minute. If the aromatics begin to stick or burn, add a tablespoon of water to loosen them.

Stir in the turmeric, followed by the diced tomato and salt. Cook, stirring frequently, until the tomatoes begin to soften and release their juices.

Drain the soaked dal and add it to the saucepan along with 3 cups of water. Bring to a boil, then reduce the heat to medium-low and simmer uncovered for 30 minutes, stirring occasionally, until the lentils are completely tender and the mixture is creamy.

Check the consistency; if the dal is too thick, stir in up to 1 cup of additional water. Stir in the garam masala and remove the pan from the heat.

Prepare the tadka by heating the oil in a small pan over medium-high heat. Add the asafetida and cumin seeds, heating until the seeds turn a shade darker and smell nutty, about 30 to 60 seconds.

Remove the small pan from the heat and swirl in the red chili powder so it blooms in the oil without burning, then immediately pour the sizzling oil over the hot dal.

Stir in the lime juice and additional salt to taste. Serve hot, garnished with cilantro.