Select the Sauté setting on the Instant Pot. After a few minutes, add the oil to heat up. Once the Instant Pot displays reads “HOT,” add the cumin seeds and mustard seeds and fry for 45 seconds, tossing frequently, until they begin to pop and are very aromatic.
Add the onions and cook until softened, about 5-6 minutes.
Add the garlic, ginger, and pepper, and cook for 90 seconds, stirring frequently to prevent burning.
Add the ground spices (turmeric, garam masala, coriander, paprika, and chili powder), curry leaves, and the 1 1/2 teaspoons kosher salt. Stir to coat and cook for 30 seconds, stirring to combine. Add the 3/4 water to deglaze, using a wooden spoon to scrape up any browned bits on the bottom of the pot.
Pour in the coconut milk, followed by the shredded jackfruit and chopped sweet potatoes. Stir to combine and select Cancel.
Secure the lid and set the Pressure Release to Sealing. Select the Pressure Cook setting at high pressure and set the cook time to 6 minutes.
Once the timer has completed, allow a natural pressure release for 10 minutes and then switch the Pressure Release knob from Sealing to Venting to release any remaining steam.
Open the pot and add the tomato sauce and spinach, and stir to incorporate. Select the Sauté setting, bring the curry to a boil, and simmer until the sauce has thickened, about 2-3 minutes. Stir in the lemon juice and cilantro.
Serve with white basmati rice or flatbread.