Set the Instant Pot to the sauté function. Once hot, add the olive oil.
Add the diced onion, carrots, and celery to the pot. Sauté for about 5 minutes, or until the vegetables begin to soften.
Stir in the minced garlic, cumin, turmeric, smoked paprika, salt, and pepper. Cook for an additional minute until fragrant.
Add the red lentils, vegetable broth, and diced tomatoes (with their juices) to the pot. Stir to combine.
Close the Instant Pot lid, making sure the valve is set to sealing. Select the manual function and cook on high pressure for 10 minutes.
Once cooking is complete, allow the pressure to release naturally for 5 minutes, then carefully perform a quick release to let out any remaining steam.
If desired, use a blender to purée some of the soup for a creamier texture and then stir in the spinach until wilted.
Finally, add the lemon juice and adjust seasoning to taste.