Preheat oven to 350 degrees. Set aside an ungreased 13x9" baking pan.
Place the cake mix, oil and just 1 egg in a large mixing bowl. Mix until well blended. Mixture should be crumbly. Reserve 1 cup for the topping. Transfer the remaining crust mixture to the pan. Using your fingertips, press the mixture evenly over the bottom of the pan so that it reaches all sides. Place the pan in the oven.
Bake the crust until it is light brown, 13 to 15 min. Remove the pan from the oven and set aside. Leave the oven on.
For the filling, place the cream cheese in the same bowl used to prepare the crust and with the same beaters (no need to clean either) blend until creamy, 30 seconds. Add the sugar, lemon juice and remaining egg. Beat on low until well combined, 1-2 min. Use a rubber spatula to spread the filling over the baked crust so it covers the entire surface. Scatter the reserved crust mixture over the filling. Place the pan in the oven.
Bake the cake until the crust is golden brown and the filling just starts to set, 14-15 min. Place the pan on a wire rack to cool for 30 min. Cut the cake into 24 bars. Remove from pan with metal spatula.
Store bars covered in plastic wrap at room temp. for up to 4 days or in the refrigerator for up to 1 week.