Preheat your oven to 180°C (350°F) and line a 20cm x 20cm (8-inch x 8-inch) square baking pan with parchment paper or grease it with a little butter or oil.
In a saucepan, melt the butter (or dairy-free margarine), brown sugar, and golden syrup over low heat. Stir until the mixture is well combined and the sugar has dissolved. Remove from heat and let it cool slightly.
In a large mixing bowl, combine the gluten-free rolled oats, gluten-free self-raising flour, gluten-free baking powder, desiccated coconut, dried fruit, chopped nuts (if using), and a pinch of salt.
Pour the melted butter, sugar, and golden syrup mixture over the dry ingredients. Add the vanilla extract and mix everything together until well combined.
Press the mixture firmly into the prepared baking pan, ensuring it's evenly spread and well compacted.
Bake in the preheated oven for about 20 minutes or until the top is golden brown and the edges start to pull away from the sides of the pan.
Remove the pan from the oven and let it cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Once completely cool, cut the oat crunchie into squares or bars.Enjoy your gluten-free oat crunchies!Please note that gluten-free ingredients can vary in texture and performance, so you may need to adjust the recipe slightly based on the specific brands and products you use. Always check that your ingredients are labeled as gluten-free if you have celiac disease or gluten sensitivity.