Turn Instant Pot to saute, add the oil, and let heat briefly.
To the heated oil, add in the onions, celery, and carrots and saute for 2-3 minutes, or until the vegetables begin to soften.
Add in lentils and garlic and saute for an additional 1 to 2 minutes. Turn Instant Pot OFF.
Add in vegetable broth and scrape up any browned bits on the bottom of the instant pot to prevent a burn warning.
Add in the crushed and diced tomatoes, oregano, coriander, cumin, salt (if using), and bay leaves.
Place the lid on the pressure cooker and be sure the vent knob is pointed towards sealed. Set cook time for 15 minutes on high pressure by hitting manual or pressure cook and using the +/- buttons to adjust the timing.
Once the cook time has elapsed, allow pressure to release naturally.
Once the pressure has been released, remove the lid. Give the soup a stir, discarding the bay leaves as you come across them. Stir in the lemon juice or balsamic vinegar and serve.
Video
Notes
Lentils: Use dried green or brown lentils, not red or yellow lentils as they can become mushy. Note on Salt: If your broth and tomatoes are not low sodium, cut the salt down to ½ teaspoon.Tomatoes: Feel free to use all crushed tomatoes or all diced tomatoes instead of a combination of the two.Storage: Lentil soup will keep in an airtight container in the fridge for 4-5 days. Alternatively, you can freeze this soup in freezer-safe containers, leaving 1 inch of room for expansion for up to 3 months.Cooking at high altitude? Use the conversion chart for cooking in the Instant Pot at High Altitude.