Line your square pan with parchment paper, leaving overhang for easy removal.
In a large mixing bowl, combine the rolled oats and sea salt, then give them a quick stir to distribute evenly.
Add the peanut butter, honey, and vanilla extract to the bowl, then stir everything together until the mixture becomes thick, sticky, and well coated—the oats should feel slightly sticky but manageable.
Melt the dark chocolate chips in a microwave-safe bowl in 30-second bursts, stirring well in between, until smooth and glossy. Let it cool slightly.
Pour the melted chocolate into the oat mixture and fold gently with a spatula until the chocolate is evenly distributed and the mixture is uniformly coated with a glossy sheen.
Transfer the mixture into your prepared pan. Use the back of the spatula or a pressing tool to evenly press and compact the mixture into the pan, about 1 inch thick, ensuring there are no air pockets.
Spread the remaining melted chocolate over the pressed mixture, smoothing it out with the spatula for a glossy, even top. Sprinkle extra oats or chopped nuts on top if desired.
Place the pan in the fridge and chill for at least 2 hours, or until the chocolate is fully set and the bars are firm to the touch.
Once chilled, lift the entire block out of the pan using the parchment overhang. Place on a cutting board and slice into 8-10 bars with a sharp knife dipped in hot water for clean cuts.
Serve immediately or store the bars in an airtight container in the fridge for up to a week. For longer storage, wrap tightly and freeze for up to 3 months.
