Select sauté on the instant pot and adjust to normal.
Add oil to the pot.
When the oil is hot add the mustard seeds and cumin seeds.
When the seeds begin to splutter, add curry leaves, whole dried red chili peppers, and asafoetida.
Add the chopped onions and sauté. Stir to prevent the onions from burning.
When the onions turn golden in roughly 2 to 4 minutes add the ginger garlic paste. Stir
Add the diced tomato and sauté for a minute until it gets mushy. Stir.
Add the salt, turmeric, red chili powder, garam masala, and serrano pepper. And ¼ cup water. Stir
Add the chopped spinach leaves and sauté for about a minute. Stir.
Add the dal, and the remaining 3 and ¼ cup water. Stir well. Make sure nothing is stuck to the bottom of the pot and scrape the bottom of the pot well.
Select manual and cook at high pressure for 7 minutes.
Use natural pressure release. The natural pressure release should take about 10 minutes.
Open the lid. If you like the dal thick then use the back of the ladle and crush some dal. You can also select sauté and stir for about 30 seconds to a minute.
Transfer in a serving bowl immediately.