Par-cook the sweet potato: Add diced sweet potatoes to a skillet with a splash of water. Cover and steam over medium heat for 4–5 minutes until slightly softened, then remove and set aside.
Sear the chicken: In the same skillet, add ghee and chicken. Cook 5–6 minutes until golden and cooked through. Remove and set aside with the sweet potatoes.
Sauté the onions: Add sliced onion to the skillet; cook 3 minutes until caramelized.
Combine everything: Return the chicken and sweet potatoes to the skillet. Add kale, garlic powder, sage, and salt. Toss to coat, then add 1 Tbsp water to help the kale wilt.
Serve: Cook another 2 minutes until everything is heated through. Finish with a squeeze of lemon and a sprinkle of fresh herbs if desired.