Preheat oven to 350 F.

In a medium sized mixing bowl, whisk together 1 3/4 cup flour, 1 teaspoon baking soda, 1 tablespoon cinnamon, 1/2 teaspoon all spice, 1/2 teaspoon nutmeg, 1/4 teaspoon ginger, 1/2 teaspoon salt, and 1 cup brown sugar. Stir in 1 cup diced apples and 1/2 cup chopped walnuts.

In a separate mixing bowl, whisk together 1 egg, 1 cup apple sauce, 1 teaspoon vanilla extract, and 1/2 cup oil.

Stir the wet ingredients into the bowl of dry ingredients until just combined. Set aside and prepare the crumble.

Using the back of a fork or your fingers, cut 2 tablespoons butter into 1/8 cup brown sugar and 1/4 cup flour until it resembles sand.

Pour the batter into a parchment paper lined loaf pan. Sprinkle the crumble evenly over the top of the batter.

Bake for 45 minutes - 1 hour, or until the cake springs back lightly like a sponge. If the cake is browning on top, but is not yet cooked through, cover with foil and continue to bake until cooked through.

Meanwhile, prepare the glaze: stir together 2/3 cup powdered sugar with 3 tablespoons milk.

Allow the cake to cool completely before drizzling with glaze.