Preheat the oven to 350 degrees F. Spray a 14-inch round cake pan with nonstick cooking spray.
Prepare cake mix according to the package instructions. Pour into the prepared cake pan and bake until set, well-browned and a toothpick inserted into the center comes out clean, about 40 minutes. Let cool completely in the pan, then invert onto a rack to remove it from the pan.
Put the vanilla frosting in a bowl. Mix 5 to 8 drops of brown food coloring into the frosting and mix until well blended for a light brown pizza crust color. Add more food coloring if need. Transfer to a pastry bag fitted with a medium round tip.
Invert the cake back onto a large round platter, pizza pan or 14-inch cardboard cake round so that it is right-side up. Cut a scored line around the cake about 3/4 inch from the edge using a paring knife, cutting only about 1/4 inch deep. Scoop out the center of the cake about 1/4 inch deep to form a shallow well and give it a raised pizza crust look. Press down on the middle of the cake to slightly compress the cake and make it less crumbly in texture. Pipe frosting over the entire cake and spread and smooth with an offset spatula. Place in the freezer to let the frosting firm up, for about 1 hour.
Meanwhile, prep the "toppings."
For "Sausage Crumbles:" Break up the chocolate rice cereal treats into chunks to resemble sausage crumbles. Set aside.
For "Pepperoni:" Unroll the fruit leather and place on a cutting board. Cut out 12 rounds from the fruit leather using a 1 1/2-inch round cutter to create pepperoni slices. Set aside.
For "Green Peppers:" Cut the green gummy candies into quarters. Set aside.
For "Mushrooms:" Roll the marzipan into a log about 6 inches long and 1 inch in diameter. Score 2 lines into the length of the log using the back of a butter knife to form the stem of the mushroom. Place in the freezer for 30 minutes to harden up.
Combine 2 drops brown food coloring with 1/4 cup of water. Remove the formed marzipan log from freezer and slice into 1/2-inch-thick slices (you should get 10 slices). Place the "mushroom" slices on a plate and paint all over with the brown food coloring and water mixture. Set aside.
For the "Tomato Sauce:" Put the strawberry jam in a microwave-safe bowl. Microwave on high until it has a pourable consistency similar to pancake batter, 30 to 45 seconds. Whisk in the red frosting until well blended. Let cool until room temperature but still pourable, about 5 minutes.
For the "Melted Cheese:" Put the cream cheese frosting in a microwave-safe bowl. Microwave on high until it has a pourable consistency similar to pancake batter, about 10 seconds. If the constancy is too thin, let it sit for 5 to 10 minutes to thicken it up.
Assemble: Remove the cake from the freezer and pour strawberry "sauce" in the center. Spread the sauce out to the edge of the crust using an offset spatula. Pour the cream cheese frosting over the sauce into individual pools to mimic the look of melted cheese, making sure to leave some of the sauce around the edge near the crust exposed. Arrange the toppings over the "melted cheese." Finish with a sprinkle of grated white chocolate to mimic grated Parmesan and chopped pistachios to mimic dried oregano. Slice and serve.