Start with instant pot on Saute mode, heat olive oil. Add onions, carrots, and celery. Saute until onion is tender (about 3-4 minutes). Stir in garlic, bay leaf, oregano, and basil; cook for 1 more minute. It takes the Instant Pot a minute to heat up, so keep that in mind.
Add lentils, broth and tomatoes. Bring to a boil. Let boil 1-2 minutes.
Switch to Instant Pot mode, put on the lid and seal the instant pot and cook on manual pressure at high for 12 minutes. It will take about 8 minutes for the pot to pressurize. After the 12 minutes is up, quick release by flipping release valve to "venting" (a little bit at a time at first.)
Once venting is finished, remove lid. When ready to serve stir in spinach and vinegar, and season to taste with salt and pepper.
Keeps in the refrigerator for 3-5 days, and freezes really well too!