Drizzle the oil into the Instant Pot and set to SAUTE. When oil is hot, add the onions and stir. Continue to cook the onions, stirring often, until the onions are very soft and beginning to brown, about 8 minutes.
Add the carrots, zucchini, salt, cumin, garlic and pepper. Sauté until the carrots and zucchini are barely soft, about 2 minutes.
Add the lentils, diced tomatoes and broth and stir.
Cover and seal the cooker and set to cook on HIGH pressure for 15 minutes. Make sure the steam release valve is in the closed position. After 15 minutes, allow the cooker to release pressure naturally. This will take about 10 to 15 additional minutes.