In a medium saucepan over low heat, combine the peanut butter, honey (or maple syrup), and vanilla extract. Stir until melted and smooth, about 3-5 minutes. Remove from heat.
In a large mixing bowl, combine the rolled oats and salt. Pour the peanut butter mixture over the oats and stir until well combined.
Line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal. Press the mixture firmly into the bottom of the dish in an even layer.
In a microwave-safe bowl, combine the dark chocolate chips and coconut oil. Microwave in 30-second intervals, stirring in between, until melted and smooth.
Pour the melted chocolate over the pressed oat mixture and spread it evenly. Refrigerate for at least 1 hour to allow the bars to set.
Once set, lift the bars out of the dish using the parchment paper. Cut into squares or rectangles and serve.