Preheat oven to 375ºF. Coat ramekins with cooking spray. Cube the challah bread and place in a large bowl. Add the raisins and walnuts. In a separate bowl, whisk the eggs, half-and-half, brown sugar, syrup, vanilla, cardamom, salt, and bourbon (if using) together until well-combined. Pour the egg mixture over the cubed bread, stirring well so that all of the bread absorbs the egg mixture. Fold in the pumpkin pulp. Divide mixture evenly among ramekins. Place all ramekins in a deep baking dish and add enough water to cover the bottom of the ramekins by one inch. Bake for 30 to 45 minutes or until the pudding is set or knife comes out clean when inserted in center. Allow puddings to cool for five minutes. Meanwhile, combine the powdered sugar and orange juice to make a glaze, whisking until smooth. Drizzle glaze over the top of each portion before serving.