For the cake: Preheat the oven to 350 degrees F. Spray a 9-inch nonstick springform pan with nonstick cooking spray.
In an electric mixer on high speed, beat the egg whites until soft peaks form. Add the sugar slowly, then the vanilla, baking powder, and salt while beating, about 2 more minutes. Turn the power off and fold in the walnuts and Maria crackers. Transfer to the prepared pan. Bake for 30 to 40 minutes.
For the frosting: In an electric mixer, beat the cream cheese, sour cream, powdered sugar, and vanilla extract until soft peaks form and the mixture is smooth.
To assemble: Remove the cake from the oven. Let cool for 15 minutes. Remove the springform. Using an offset spatula, spread the frosting all over the cake. Garnish with the strawberries and serve.