In a small pot on the stove, heat maple syrup and nut butter over medium. Stir consistently and cook until bubbling and melted together, a couple of minutes. Remove from heat and stir in vanilla extract. Let cool slightly.

In a large bowl, mix quick oats, crispy rice if using, and salt. Slowly stream in cooled nut butter mixture and stir to combine. Add in chocolate if using.

Line an 8x8 pan with parchment paper or reusable food wrap. Press oat mixture into the pan tightly, using the back of a spoon or the bottom of a glass to compress firmly. Make sure you press it evenly into the corners to make as sharp of edges as possible. If desired, press more chocolate onto the top of the bars.

Freeze bars for 10 minutes, until solid. Remove from freezer, lift edges of parchment, and remove block of bars. Carefully using a sharp knife, cut into 12 bars. Store in a sealed container in the fridge or on the countertop for 5 days.