Preheat the oven to 300 F (150 C).
Grease an 8-inch (20 cm) square baking dish and line it with parchment paper.
In a saucepan, heat the brown sugar, butter, and maple syrup over low heat, stirring regularly until the butter is melted.
Remove the saucepan from the heat, then stir in the rolled oats. Mix well.
Pour the mixture into the prepared baking dish and press it down with a wooden spoon.
Bake for 45 minutes.
Let the dish cool for 10 minutes.
Top with dulce de leche and refrigerate until it has set.
Melt the chocolate in a double boiler and stir in the sunflower oil.
Pour the chocolate mixture over the dulce de leche and smooth it out with a spatula.
Let it cool to room temperature until the chocolate has set.
Cut into 16 squares using a knife that has been passed under hot water between each cut.