Turn the Crock Pot on high, and place the lid on top to let it warm up.
In a bowl, add the flour, salt, baking powder, and cocoa, and mix well to blend.
In the mixing bowl of a stand mixer, add the sugar, eggs, milk, vanilla, and melted butter, and blend on low speed for about 1 - 2 minutes.
When all ingredients are combined, and sugar is dissolved, add the flour mixture a little at a time, blending between additions, and mixing all ingredients until well blended. Scrape down the sides of the mixing bowl, and blend again.
Spray the inside of the Crock Pot with the cooking oil spray, and pour the cake batter into the Crock Pot. Place the lid on the Crock Pot, and allow 1 hour for the cake to bake.
After an hour, check the cake, but inserting a toothpick in the center, and making sure it comes out clean.
When the cake is done, sprinkle the crushed graham crackers all over the top of the cake. Drizzle the chocolate fudge syrup all over the graham cracker crumbs, and pour the mini marshmallows on top, and add a generous amount of syrup, drizzled on the marshmallows. Place the lid back on the Crock Pot, turn the heat to low, and let the cake sit until the marshmallows have melted, about 15 - 20 minutes.
When the marshmallows have melted, drizzle a little more chocolate syrup on top, and serve in individual bowls, or on dessert plates. Enjoy!