Preheat your oven to 180°C (350°F). Line your 8x8 inch baking dish with parchment paper, leaving overhang for easy removal.
In a large bowl, combine the oats and cinnamon, then stir to distribute the spice evenly.
In a small saucepan, melt the butter over medium heat until bubbling gently, then remove from heat.
Stir in the honey and vanilla extract into the melted butter until smooth and fragrant.
Pour the warm mixture over the oats and cinnamon, then stir until all the oats are coated and the mixture feels sticky.
Transfer the mixture to your prepared baking dish and press down firmly with the back of a spatula to create an even, compact layer.
Bake in the oven for 20-25 minutes, until the edges are golden and the aroma is warm and toasty.
Remove the baking dish from the oven and let the bars cool in the pan for about 10 minutes, allowing them to firm up slightly.
Using the parchment overhang, lift out the entire slab and transfer it to a wire rack to cool completely for about 30 minutes.
Once cooled, cut into squares or rectangles with a sharp knife. Handle gently, as they can be crumbly until fully cooled.
Enjoy these rustic, chewy cinnamon oat bars as a comforting snack or breakfast treat, storing leftovers in an airtight container at room temperature for up to 4 days.