Select the Saute function and add the olive oil to the Instant Pot.
Saute the onions until they are softened and slightly translucent.
Add the garlic and saute for about 30 seconds more.
Next add the carrots and celery and saute for a few minutes until the vegetables are softened.
Add the bay leaf, thyme, potatoes, lentils, and vegetable broth (or water) and stir to combine.
Close the lid and set the timer for 7 minutes on Manual (Pressure Cook on High).
Allow the pressure to release naturally.
After the pressure has released, remove the lid and stir in the spinach.
Add salt and pepper, to taste, and enjoy.
Notes
Keep in mind that it will take time for the Instant Pot to come up to pressure and come down from pressure before and after the 7 minutes start.
Leftover soup can be covered and refrigerated for 3 to 4 days. Or you can freeze it for up to 3 months.
Stovetop instructions: Add an extra cup of liquid and simmer for 30 to 40 minutes until the lentils and potatoes are soft. Remove from the heat and stir in the spinach.