Start the instant pot in SAUTE mode and heat oil in it.
Add onions and garlic. Mix and saute for about 3 minutes. Then add tomatoes and saute for another minute.
Add carrots, celery and all the spices.
Add the lentils and broth. Stir it all up. Press Cancel and close the lid with vent in sealing position.
Set the instant pot to pressure cook on high pressure for 18 minutes. When the instant pot beeps, release the pressure naturally. Press Cancel.
Add in spinach, lemon juice and sugar. Add some red chili flakes if you like. Stir it all up. Brown Lentil Soup is ready to enjoy!