Line an 8x8 inch square baking pan with parchment paper, leaving an overhang on two sides for easy removal.
In a large mixing bowl, whisk together the rolled oats, protein powder, ground flaxseed, and cinnamon.
Add the almond butter and honey to the dry ingredients, stirring until the mixture becomes thick and crumbly.
Gradually add the almond milk one tablespoon at a time, mixing until the dough is moist enough to stick together when pressed.
Fold in the mini dark chocolate chips until evenly distributed.
Transfer the mixture to the prepared pan and press down firmly using a spatula or the bottom of a glass to create an even, compact layer.
Refrigerate the pan for at least 60 minutes to allow the bars to set and the oats to hydrate.
Lift the parchment paper to remove the slab from the pan and slice into 12 rectangular bars with a sharp knife.