Preheat oven to 350 degrees F.
Line 8x8” baking dish with foil or parchment paper and spray with cooking spray.
In a bowl with electric mixer, beat together butter and brown sugar until well combined, about 1 minute.
Add in flour, oats, baking powder, salt, and cinnamon and mix until crumb mixture forms.
Press half of the mixture on the bottom of the prepared pan.
In a separate bowl, whisk together the sweetened condensed milk, orange zest, and orange juice.
Pour orange mixture on top of crust.
Sprinkle with remaining crumb mixture.
Bake in preheated oven for 30-32 minutes, until golden on the edges and set in the middle. It will still seem kind of jiggly but it will set up as it cools.
Cool completely.
Remove bars from the pan with the foil and peel foil from edges. Cut into bars.
Enjoy!