Turn on a multi-functional pressure cooker (such as Instant Pot(R)) and select Saute function. Heat olive oil; cook and stir until the onion has softened and turned translucent, about 5 minutes. Add carrots and celery and cook until tender, about 3 minutes. Combine lentils, diced tomatoes, vegetable broth, garlic, thyme, salt, paprika, and black pepper in the pot. Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 15 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure using the natural-release method according to manufacturer's instructions, 10 to 40 minutes. Serve in bowls and sprinkle with parsley.
