Heat the olive oil in a large pot over medium heat. Add the ground beef and cook until browned, breaking it up with a spoon as it cooks.
Add the diced onion and minced garlic to the pot. Cook for 3 to 4 minutes until the onion softens.
Stir in the cubed sweet potatoes, dried thyme, salt, and black pepper. Cook for 2 minutes to coat everything evenly.
Pour in the beef broth and bring the mixture to a boil. Reduce the heat to low, cover the pot, and simmer for 20 minutes until the sweet potatoes are tender.
Add the chopped kale and stir until it wilts, about 3 minutes. Remove the pot from the heat and let the stew sit for 5 minutes before serving.