Heat olive oil in the Instant Pot using the 'sauté' setting. Add the chopped onion and celery, cooking until they're softened, which should take about 5 minutes.
Stir in the minced garlic, tomato paste, ground cumin, and dried thyme, letting them cook together for another minute to release their flavors.
Pour in the water, scraping any browned bits off the bottom of the Instant Pot. This will prevent a burn notice and add flavor to your soup. Turn off the 'sauté' function.
Add the vegetable broth, diced tomatoes, chopped carrots, and lentils to the pot. Season the mix with salt and pepper, and add bay leaves if you're using them.
Seal the Instant Pot lid and set the valve to the 'sealing' position. Select the 'manual' setting on high pressure for 16 minutes. For softer lentils, like brown ones, set for 12 minutes. After cooking, allow the pressure to release naturally for 5 minutes, then manually release any remaining pressure.
Open the Instant Pot and stir in the baby spinach or kale until wilted. Serve the soup with a squeeze of lemon juice, a sprinkle of chopped parsley, and a dusting of parmesan cheese, if desired.