Set the Instant Pot to saute mode and add the olive oil. Cook the onion and garlic for 3 minutes until softened.
Add the lentils, vegetable broth, oregano, salt, and black pepper. Stir to combine.
Secure the lid and set the Instant Pot to high pressure for 15 minutes. Allow a natural pressure release for 10 minutes, then quick release any remaining pressure.
Stir in the olives, lemon zest, and lemon juice. Let the stew sit for 2 minutes to warm through.
Ladle into bowls and top with fresh parsley before serving.