Line your baking pan with parchment paper, leaving a slight overhang for easy removal.
Combine the dark chocolate chips and butter or coconut oil in a microwave-safe bowl. Microwave in 30-second bursts, stirring after each, until the mixture is smooth and glossy.
Pour the oats into a large mixing bowl. Add the sea salt and any optional add-ins like chopped nuts or dried fruit.
Pour the melted chocolate mixture over the oats. Use a spatula to fold everything together until the oats are fully coated and the mixture feels sticky and well combined.
Transfer the mixture into the prepared pan. Press it down firmly with the back of the spatula or a piece of parchment to create an even, compact layer about 1 inch thick.
Refrigerate uncovered for at least 2 hours, or until the bars are firm and shiny. For quicker setting, place the pan in the freezer for about 1 hour.
Once set, lift the entire block out of the pan using the parchment overhang. Use a sharp knife to cut into even squares or rectangles.
Optional: sprinkle a pinch of flaky sea salt on top of the bars before serving for an extra flavor boost.
Enjoy your chewy, glossy chocolate oat bars immediately, or store them in an airtight container in the fridge for up to a week. For longer storage, freeze and thaw before serving.
