Heat the olive oil in a large pot over medium heat. Add the sliced sausage and cook until browned on both sides. Remove the sausage and set it aside.
Add the onion, garlic, and carrots to the same pot. Cook for 4 to 5 minutes until the onion softens.
Stir in the butternut squash and apple. Cook for 2 minutes to let the flavors start to combine.
Add the lentils, chicken broth, and dried sage. Bring the mixture to a boil, then reduce to a simmer.
Return the sausage to the pot. Cover and simmer for 30 minutes, stirring occasionally, until the lentils and squash are tender.
Season with salt and pepper. Serve hot.