This healthy Lentil Soup is as easy as it gets-- simply pour the ingredients into an electric pressure cooker, like the Instant Pot, and press a button. With no added oil, and loads of vegetables included, it makes a nutritious vegan or vegetarian meal.
In the bowl of the Instant Pot, combine the onion, carrots, celery, tomatoes, garlic, cumin, curry, cayenne (if using), lentils, water, and several grinds of black pepper. Do not add any salt yet. Stir well to combine.
Secure the lid and move the steam release valve to Sealing. Use the Manual or Pressure Cook button to cook for 10 minutes at high pressure. It should take 10 to 15 minutes for the pot to come to pressure, then the cooking cycle will begin to countdown.
When the cooking cycle is complete, allow the pressure to naturally release for 10 minutes, then move the steam release valve to Venting. When the floating valve drops, it's safe to remove the lid.
Give the soup a stir to make sure the lentils and vegetables are tender, then stir in 1 teaspoon of salt and the chopped fresh spinach. The greens should wilt quickly in the hot soup. Season with additional salt to taste, then serve warm with slices of lemon to help brighten the flavor even more.
Leftover soup can be stored in an airtight container in the fridge for up to a week.