Preheat the oven to 350°F. Heat the olive oil in a Dutch oven over medium heat on the stovetop.
Add the beef stew meat and brown it on all sides for about 5 minutes. Remove the meat and set it aside.
Add the onion, carrots, and garlic to the pot. Cook for 4 minutes until the onion softens.
Stir in the lentils, beef broth, diced tomatoes, thyme, salt, and black pepper. Return the beef to the pot and bring the mixture to a simmer.
Add the sweet potatoes and stir to combine. Cover the Dutch oven and transfer it to the oven.
Bake for 1 hour. Remove the pot, stir in the kale, and return it to the oven uncovered.
Bake for another 20 minutes until the kale wilts and the lentils are tender.