Line your square pan with parchment paper, leaving some overhang for easy removal.
In a microwave-safe bowl, combine the peanut butter, honey, and vanilla. Microwave in 30-second bursts, stirring in between, until the mixture is smooth, gooey, and fragrant—about 1 minute total.
Add the oats and a pinch of salt to the melted mixture. Mix thoroughly with a spatula until everything is evenly combined and sticky.
Press the oat mixture evenly into the prepared pan, using the back of a spatula or your fingers to smooth the surface—this helps create a compact, chewy base.
Chop the chocolate into small pieces if using bars. Melt the chocolate chips or chopped chocolate with the coconut oil in short bursts in the microwave, stirring until smooth and shiny—about 30 seconds each time.
Pour the melted chocolate over the pressed peanut butter oat layer, spreading it evenly with a spatula to cover all surfaces completely.
Refrigerate the pan for at least 2 hours, or until the chocolate is firm and the entire layer is set. The bars will firm up and be ready to cut.
Once chilled, lift the bars out of the pan using the parchment overhang. Slice into 12 equal pieces with a sharp knife, pressing down firmly but gently to keep clean edges.
Serve immediately or store in an airtight container in the fridge. For a softer bite, let the bars sit at room temperature for 10 minutes before eating.