Select the Sauté setting on the Instant Pot and after a few minutes, add the olive oil. Once the oil has heated up, add the onion. Cook until the onion is browned and completely soft, 6 to 8 minutes.
Add the carrots and garlic along with 1 teaspoon of the kosher salt, and black pepper to taste. Cook until the carrots are just starting to soften, 2 to 3 minutes.
Add the vegetable broth, lentils, potatoes, bouquet garni, and and the remaining 1/2 teaspoon kosher salt, and stir gently. Then pour the crushed tomatoes on top, but don’t stir (the tomatoes will get incorporated during the pressure cooking). Select the Cancel setting.
Secure the lid and set the valve to Sealing (not Venting). Select the Pressure Cook setting (or Manual setting on older models) at high pressure and set the cook time to 12 minutes.
Once the 12-minute timer has completed and beeps, allow a natural pressure release.
Open the pot and remove the bouquet garni. Stir in the dijon mustard and balsamic vinegar and taste. Add more salt and pepper to taste.