Heat the olive oil in a large pot over medium heat. Add the beef pieces and cook until browned on all sides.
Add the diced onion and minced garlic to the pot. Stir and cook for 3 minutes until the onion softens.
Stir in the butternut squash cubes and chopped sage. Cook for 2 minutes to coat everything in the oil.
Add the rinsed lentils, beef broth, salt, and black pepper. Stir to combine.
Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 40 minutes, stirring once or twice, until the beef and lentils are tender.