Heat oven to 375 degrees. Butter 9-inch square baking pan.
Toss apples with granulated sugar and both gingers. Add lemon zest and juice and toss again. Spread apples evenly in buttered pan.
Coarsely chop nuts and mix with oats, flour, brown sugar, cinnamon, and salt in mixing bowl. Cut in butter with pastry blender until mixture resembles very coarse crumbs. (Or coarsely chop nuts in food processor. Add dry ingredients and pulse several times to mix. Place butter on top and pulse until mixture resembles very coarse crumbs.) Sprinkle topping over apples.
Bake until apples are tender and topping is browned, 45-50 minutes. Serve warm with whipped cream.