Heat the vegetable oil in a large pot over medium heat.
Add the cumin seeds and mustard seeds to the hot oil and cook until they start to pop, about 1 minute.
Add the chopped onion, garlic, ginger, and green chili to the pot. Sauté until the onion is soft and translucent, about 5 minutes.
Stir in the turmeric powder, ground coriander, garam masala, and chili powder. Cook for 1 minute to release the spices’ aroma.
Add the rinsed red split lentils and basmati rice to the pot and stir well to coat them with the spices and onion mixture.
Pour in 4 cups of water and add salt. Stir to combine.
Bring the mixture to a boil, then reduce the heat to low, cover the pot, and simmer for 25-30 minutes, or until the lentils and rice are tender and the water is absorbed.
Remove the pot from heat and let it sit covered for 5 minutes.
Fluff the dhal rice gently with a fork and stir in the chopped cilantro leaves before serving.