Blend flour, sugars, cinnamon, and salt in a food processor until combined well. Add butter and blend until mixture forms large clumps. Transfer to a bowl and work in pecans with your fingertips. Preheat oven to 375°F. Whisk together sugar and cinnamon in a large bowl. Peel, quarter, and core apples, then slice 1/2 inch thick. Add apples to sugar mixture along with lemon juice and orange zest and toss until combined well. Spread apples in a lightly buttered 3 1/2- to 4-quart shallow baking dish and crumble topping evenly over them. Bake in middle of oven until topping is golden brown, about 1 hour. Cool to warm and serve with ice cream.