Preheat oven to 350 degrees F. Coat an 8x8-inch square baking dish with cooking spray and set aside.
In a medium bowl, combine the flour, salt and baking powder. In a large bowl, using a hand-held mixer, mix the butter and brown sugar until well combined. Gradually add the flour mixture, mixing until incorporated.
Press half of the crumb mixture into the bottom of the prepared pan. Add the oats to the other half of the mixture still in the bowl. Mix well and set aside.
In a separate bowl, use a hand mixer to combine the sweetened condensed milk, cream cheese, lemon juice and lemon zest until creamy. Spread over top of the pressed crumb mixture in the pan.
Top with the other half of the crumb mixture. Bake in the preheated oven for 20-25 minutes, or until golden brown. Let cool, cut into squares and store in refrigerator.