Preheat the oven to 180 degrees Celsius. Line a 9×13 inch baking pan with parchment paper, leaving extra over the sides for easy removal.

In a large bowl, combine flour, sugar, baking powder, salt, and cinnamon. Mix well so the ingredients are evenly distributed.

Add melted butter and the egg to the dry mixture. Stir using a fork or spatula until a crumbly dough forms.

Transfer two thirds of the crumb mixture into the prepared pan. Press it down firmly and evenly to create a solid base layer.

In another bowl, mix diced peaches, sugar, lemon juice, and cornstarch. Stir gently until the peaches are evenly coated.

Spread the peach filling evenly over the base layer. Use a spoon to ensure the fruit is evenly distributed.

Sprinkle the remaining crumb mixture evenly over the top of the peaches. Do not press it down.

Bake in the preheated oven for 40 to 45 minutes, or until the top is golden brown and the filling is bubbling slightly at the edges.

Remove from the oven and allow the bars to cool completely in the pan.

Once cooled, lift the bars out using the parchment paper. Place on a cutting board and slice into even squares before serving.