Select sauté on the instant pot and adjust to normal. Add oil to the pot.
When oil is hot (in about 30 seconds), add mustard seeds, cumin seeds, curry leaves, urad dal, and chana dal.
When the mustard seeds and cumin splutter add the chopped onions and ginger garlic paste.
Keep stirring in order to prevent the onions from burning. When the onions turn slightly golden in about 2 to 3 minutes add ground turmeric, ground coriander, ground cumin, and salt. Give it a good stir.
Add the diced potatoes and stir well.
Add Serrano peppers, garam masala and water. Give it a good stir.
Press cancel. Close the lid and select manual/high pressure for 4 minutes. When done quick release the pressure and open the lid right away. Finally add the lemon juice and cilantro.
Serve with tortilla, rice, naan or dosa.