Preheat the oven to 350°F (175°C).
In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition, then mix in 1 teaspoon vanilla extract.
In a separate bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Stir in the rolled oats until evenly incorporated.
Press the oatmeal cookie dough evenly into a 12-inch round pizza pan or a rimmed baking sheet to form the cookie crust.
Bake in the preheated oven for 12 to 15 minutes, or until the edges are golden brown and the center is set.
Remove from the oven and allow the cookie crust to cool completely in the pan on a wire rack.
While the cookie crust cools, prepare the cream cheese frosting by beating the softened cream cheese, powdered sugar, and 1 teaspoon vanilla extract together until smooth and creamy.
Once the cookie crust is completely cooled, spread the cream cheese frosting evenly over the top.
Arrange the sliced strawberries, blueberries, kiwi, mandarin orange segments, and halved grapes evenly over the cream cheese layer to create a colorful fruit topping.
Refrigerate the assembled fruit pizza for at least 30 minutes before slicing and serving to allow the frosting to set.