Rinse and remove any stones or debris from the lentils. Prep the vegetables for the soup base.
Turn the Ninja Foodi or Instant Pot on high sear/sauté. Add in olive oil and when it is hot, add in the soup base onions, carrots, and celery. Stir to combine. Add in the smashed and peeled garlic cloves and the lentils. Add in the seasonings and stir. Sauté for 5 minutes.
Deglaze the pot with 4 cups of water and stir well. Add in the tomatoes with the juice and stir. Put the pressure lid on and turn the valve to seal. Set the pressure on high for 5 minutes. When the time is up, immediately release the pressure and when the pin drops, open the lid.
Add in the mushrooms and the rest of the soup vegetables EXCEPT for the spinach. Stir and put the pressure lid back on and turn the valve to seal. Pressure cook on high for 1 minute. When the time is up do an immediate release. When the pin drops, open the lid.
Add the spinach and stir it into the soup to wilt. Taste for seasonings and adjust as necessary.