Preheat the oven to 350°F. Grease a 12-inch round (rimmed) pizza pan with nonstick spray; set aside. (You can also use the disposable round pizza pans.)
In a medium mixing bowl, combine the brownie mix, eggs, water and oil. Stir until just combined. Pour into the greased pan and spread evenly with a spatula. Bake for about 25 minutes, or until a toothpick inserted in the center comes out clean. Remove the brownie pan from the oven and allow to completely cool in the pan on a wire rack.
In a medium bowl, cream together the cream cheese and powdered sugar until smooth. Spread evenly over the top of the cooled brownie round. Slice the bananas and sprinkle with lemon juice to preserve the coloring. Place the banana slices evenly over the top of the cream cheese layer. Sprinkle with strawberries and blueberries.
Slice into wedges and serve immediately with a dollop of COOL WHIP whipped topping.