Preheat the Instant Pot on Sauté mode, add olive oil, then cook chopped onion and garlic until translucent and fragrant, about 3–4 minutes.

Stir in brown lentils, diced tomatoes, vegetable broth, diced carrots (if using), salt, pepper, and red pepper flakes. Scrape any browned bits for extra flavor.

Lock the lid and set to High Pressure for 15 minutes. Allow a natural pressure release for 10 minutes before carefully releasing any remaining steam.

Open the lid, fold in fresh basil leaves until wilted and bright green. Taste, then adjust salt and pepper to suit your preference.

Ladle stew into bowls, offering grated Parmesan cheese and extra basil leaves on top. Serve with crusty bread for dipping.