Heat sesame oil in a large skillet or wok over medium heat. Add ginger and garlic; cook for 30 seconds, or until fragrant, stirring constantly. Add kale and stir until coated with oil. Stir in soy sauce and orange juice; cover and cook for 3 minutes, or until kale is softened.
Stir in sesame seeds and red pepper flakes (if using) and serve.