In a medium mixing bowl, combine the rolled oats, peanut butter, honey (or maple syrup), chocolate chips (if using), vanilla extract, and salt. Stir until all ingredients are well mixed and form a sticky mixture.
Line a muffin tin with paper liners or lightly grease it with cooking spray.
Divide the mixture evenly among the muffin cups, pressing down firmly to pack them in.
Refrigerate the cups for at least 30 minutes to set.
Once set, remove the cups from the muffin tin and enjoy! Store any leftovers in an airtight container in the refrigerator for up to one week.