Press the "sauté" button on your Instant Pot. Add the oil to the pot.
Add the onion. Sweat the onion for 5 minutes, until it becomes soft and translucent, stirring frequently.
Add the garlic, ginger, cumin seeds and mustard seeds. Sauté everything with the onion for about 1 minute, stirring constantly, until the mixture becomes very fragrant.
Press the "cancel" button.
Stir in the broth, pigeon peas, turmeric, cumin, garam masala, and cayenne pepper.
Secure the lid on the Instant Pot and set the valve to the "sealing" position. Press the "pressure cook" or "manual" button and set the pressure to high. Set the Instant Pot to cook for 15 minutes. (Note 1)
When the dal has finished cooking carefully more the valve to the "venting" position and allow the pressure to release completely.
Remove the lid from the Instant Pot. The dal should still be simmering at this point.
Begin stirring in the spinach, a handful at a time, allowing each handful to wilt before adding the next. If the dal cools down too much and stops simmering you can set the Instant Pot to the "soup/broth" setting just until the spinach has cooked.
Allow the spinach to cook just until wilted, about 5 minutes, then stir in the lemon juice and season the dal with salt and pepper to taste.
Serve with basmati rice and sprinkle with fresh cilantro.