Line an 8-inch square baking tray with parchment paper
Place the oats in a food processor fitted with the steel blade and process until ground into a flour.
Add the protein powder, cocoa powder (or more protein powder), nut butter, maple syrup, salt, 1/4 cup milk and melted unsweetened chocolate.
Process until the mixture is well-combined and is tacky (but not sticky) to the touch.
Add more milk by the teaspoonful and process, only as necessary for the mixture to reach the proper consistency.
Transfer the mixture to the prepared pan and press firmly into an even layer, smoothing the top as much as possible.
Cover with parchment and place in the refrigerator for about 1 hour.
Remove the bars from the pan and slice into 10 or 12 equal-sized rectangular bars.
Drizzle some melted chocolate over the top, and allow to sit at room temperature until set.
Store in the refrigerator.