Make the Topping: Combine the flour, pecans, oats, brown sugar, granulated sugar, cinnamon and salt in a medium bowl. Stir in the butter until the mixture is thoroughly moistened and crumbly. Set aside while preparing the filling.
Make the Filling: Toss the apples, granulated sugar and cinnamon together in a large bowl; set aside. Bring the apple cider to a simmer in a 12-inch ovensafe skillet over medium heat; cook until reduced to ½ cup, about 5 minutes. Transfer the reduced apple cider to a small bowl or liquid measuring cup; stir in the lemon juice and set aside.
Heat the butter in the now-empty skillet over medium heat. When the foaming subsides, add the apple mixture and cook, stirring frequently, until the apples begin to soften and become translucent, 12 to 14 minutes. (Do not fully cook the apples.) Remove the pan from the heat and gently stir in the apple cider mixture until the apples are coated.
Sprinkle the topping evenly over the fruit, breaking up any large chunks. Place the skillet on a baking sheet and bake until the fruit is tender and the topping is deep golden brown, 15 to 20 minutes. Cool on a wire rack until warm, at least 15 minutes, and serve with vanilla ice cream or whipped cream.