Melt butter in a skillet over medium heat. Add sliced apples. Cover and reduce heat to low. Fry for 3-4 minutes. Turn apples. Sprinkle with sweetener, cinnamon, and salt. Cover. Fry 2 minutes or until desired tenderness. Set aside. Mix Greek yogurt with collagen. Spoon into two dessert bowls. Top with apples. Serves 2.