Preheat your oven to 180°C (350°F). Line the baking pan with parchment paper, leaving overhang for easy removal.
In a medium bowl, combine the oats, flour, salt, and brown sugar. Stir until evenly mixed, creating a crumbly dry mixture.
Melt the butter in a saucepan over low heat until just melted and fragrant. Pour the melted butter into the dry mixture and stir until the mixture becomes crumbly and moist.
Press about two-thirds of this oat mixture into the prepared pan, using the back of a spoon or your fingers to create an even, firm crust.
Sprinkle the dried cranberries evenly over the crust. Tossing them in a bit of flour beforehand helps prevent sinking during baking.
If using, sprinkle lemon zest over the cranberries to brighten the tartness and add a fresh aroma.
Crumble the remaining oat mixture over the cranberries, pressing it gently into the filling to create a layered topping.
Bake in the preheated oven for 25-30 minutes, until the topping is golden brown and the cranberries are bubbling around the edges.
Remove the pan from the oven and let the bars cool in the pan for about 15 minutes. This helps them set and become easier to slice.
Lift the bars out of the pan using the parchment overhang and transfer to a wire rack to cool completely before slicing into squares.
Slice into squares and serve at room temperature. Enjoy the rustic, tart, and buttery flavors with a cup of tea or coffee!
