Preheat your oven to 350°F (175°C). Grease an 8x8-inch baking dish with cooking spray or line it with parchment paper for easy removal.
In a mixing bowl, combine flour, rolled oats, baking powder, baking soda, salt, and cinnamon. Mix until well combined.
In a separate bowl, whisk together the melted butter, brown sugar, egg, and vanilla extract until smooth.
Gradually add the dry ingredients to the wet mixture, stirring until just combined. If using pecans, fold them in now.
Pour the mixture into the prepared baking dish and spread it evenly with a spatula.
Bake in the preheated oven for 20-25 minutes, or until the edges are golden and a toothpick inserted in the center comes out clean.
While the bars are baking, prepare the cream cheese frosting by combining softened cream cheese, powdered sugar, and milk in a bowl. Mix until smooth and creamy; adjust the milk for desired consistency.
Once the bars are baked, allow them to cool in the pan for about 10 minutes, then spread the cream cheese frosting evenly on top.
Allow the bars to cool completely before slicing them into squares.
Notes
Dust the top with extra powdered sugar and sprinkle some additional chopped pecans for an added crunch before serving. Consider serving these bliss bars on a decorative platter, garnished with fresh cinnamon sticks for a delightful visual touch!