Preheat oven to 325°F and grease a 8×8 pan with baking spray. Line the bottom with parchment paper, set aside.
In a large saucepan, combine water and raisins and bring to a gentle boil, cooking for 10 minutes. Add vegetable oil to the boiled mixture. Allow the mixture to cool to room temperature.

Combine flour, sugar, pumpkin spice mix, baking soda, and salt in a bowl, whisking to break up any lumps.
Mix the dry-ingredients into the boiled raisin mixture. Add in egg and walnuts (if using).
Pour batter into prepared pan and bake until a toothpick inserted comes out mostly clean with a few moist crumbs about 35 to 40 minutes. Cool completely before assembling.
TO MAKE THE FROSTING:
In a large, bowl beat cream cheese and butter until smooth and lump free, about 2 to 3 minutes. Gradually add powdered sugar and salt, beating until smooth.
TO ASSEMBLE THE A&P SPANISH BAR:
Remove the cake from the baking pan and place it on a cutting board.
Slice the cake in half.
Transfer one layer to a serving tray and apply the frosting on top.
Top with the second layer and top with remaining frosting.

For a grooved pattern, use a fork to draw lines in the frosting.