Peel the sweet potato and cut it into small 1/2-inch cubes to ensure even cooking.
Heat a large cast-iron skillet over medium-high heat and add the ground beef, breaking it apart with a spatula until fully browned.
Transfer the cooked beef to a plate and set aside, leaving any rendered fat in the skillet.
Add the olive oil to the skillet followed by the sweet potato cubes, spreading them out in a single layer.
Cook the potatoes undisturbed for 5 minutes to develop a golden-brown crust, then stir in the diced onion and red bell pepper.
Continue cooking for 6-8 minutes, stirring occasionally, until the sweet potatoes are fork-tender.
Stir in the minced garlic, rosemary, thyme, sea salt, and black pepper, sautéing for 1 minute until the aromatics are fragrant.
Return the beef to the skillet and add the chopped kale, tossing everything together for 2 minutes until the kale is wilted and the hash is piping hot.