Prepare the pan. Preheat your oven to 350°F. Lightly spray a Bundt pan with nonstick cooking spray, then set the pan on a baking sheet. The baking sheet helps catch any buttery brown sugar mixture that decides to escape during baking.
Make the cinnamon sugar. In a small bowl, combine the brown sugar, cinnamon, allspice and salt. Stir until everything is evenly mixed. Melt the butter in a microwave-safe bowl for about 1 minute and set it aside.
Cut the biscuits. Separate the refrigerated biscuits and cut each biscuit in half, then in half again, creating 4 equal pieces from each biscuit.
Prepare the apples. Dice the apples into small, bite-size pieces. You don't have to peel them first, but you can if you prefer.
Start the first layer. Sprinkle a light layer of diced apples and walnuts into the bottom of the Bundt pan.
Coat the biscuit pieces. Dip each biscuit piece into the melted butter, then roll it generously in the brown sugar mixture until well coated.
Build the first layer. Place the coated biscuit pieces into the Bundt pan over the apples and walnuts. Continue until you have an even layer around the pan.
Keep layering. Sprinkle about one-third of the remaining apples and walnuts over the biscuit layer. Continue dipping the biscuit pieces in butter and brown sugar, adding them to the pan and layering with the remaining apples and walnuts. You should end up with about three layers.
Bake the monkey bread. Place the Bundt pan on the baking sheet and bake for about 35 minutes, or until the biscuit pieces in the center are cooked through.
Let it rest before flipping. Remove the monkey bread from the oven and let it sit in the pan for 10 minutes. This gives the buttery sugar mixture a chance to settle and makes the bread easier to release.
Flip it out. Place a large serving plate upside down over the Bundt pan. Carefully flip the pan and plate together, then gently wiggle the Bundt pan until the monkey bread releases onto the plate.
Make the icing. While the monkey bread is resting, sift the powdered sugar into a small bowl. Whisk in the vanilla extract and milk until smooth and drizzleable.
Drizzle and serve. Drizzle the vanilla icing generously over the warm Apple Fritter Monkey Bread and serve.