On “Saute” mode, add olive oil until it’s hot but not smoking. Cook the onions until they’ve softened and are slightly browned.
Then, add the celery, carrot, garlic, oregano, and thyme. Cook for about 5 minutes, then add in the tomato paste. Stir until all of the ingredients are combined.
Finally, add the veggie broth, red lentils, walnuts, and crushed tomatoes. Stir to ensure all of the ingredients are evenly mixed.
Set the Instant Pot to Pressure Cook (or Manual) on High Normal for 20 minutes. While the Instant Pot is cooking the lentil bolognese, this would be a good time to cook your pasta according to its packaging. Once the Instant Pot beeps, allow it to naturally release pressure for about 10 minutes.
Remove the lid and stir in balsamic vinegar and season with salt and pepper to taste. Serve immediately over your cooked pasta and garnish with fresh parsley and/or basil!