Preheat the oven to 350 degrees F. Butter a 2-quart baking dish.
For the filling: Toss the apples, butterscotch chips, brown sugar, flour, cinnamon, allspice, and lemon juice together in a large bowl. Add to the buttered baking dish and dot with butter.
For the topping: In a separate bowl, combine the flour, sugar, oats, and salt. Blend the butter into the mixture until it forms pea size lumps. Stir in the pecans and sprinkle over the filling.
Bake until the apples are tender and butterscotch is bubbling, about 45 minutes. Let cool for 5 minutes before serving. Plate with a scoop of butter pecan ice cream on top.