Set Instant Pot to Saute setting. Add the oil. Add the sausages and brown them on at least two sides, for about 5 minutes total. They won't be completely cooked through yet.
Cancel the Saute setting. Remove the sausages and set them aside on a cutting board. If there's an excess of fat in the pot, drain it off now.
Add all of the remaining ingredients to the Instant Pot.
1½ cups green lentils,, 4 cups water, 28 ounces canned crushed tomatoes, 3 cups sweet potatoes,, ½ teaspoon ground black pepper, ½ teaspoon garlic powder, ¾ teaspoon fine sea salt, 1 teaspoon dried oregano, 1½ teaspoons onion powder, 1½ teaspoons smoked paprika
Cut the semi-cooked sausages into bite-sized chunks, and return them to the Instant Pot.
Put the lid on the Instant Pot, and set the vent to seal for pressure cooking. Cook on High Pressure for 6 minutes. (It will take about 22 minutes for the Instant Pot to reach full pressure.) Allow a slow release for 15 minutes.
Carefully open the vent to release the remaining pressure. Stir the soup, and serve.
Notes
One pound of sausage is enough, if that's how yours comes packaged.
You may substitute ground beef for the sausage, but it will lack the flavour of the sausage.
You may substitute chunks of peeled butternut squash or carrot for the sweet potato.