In a large bowl, mix oats, protein powder, chia or flax seeds (if using), and sea salt.,In a separate bowl, stir together nut butter, honey or maple syrup, and vanilla extract until smooth.,Combine the wet and dry ingredients until a thick dough forms. Add milk one tablespoon at a time if needed to bind.,Fold in chocolate chips or dried fruit if using.,Press the mixture into a parchment-lined pan and refrigerate for 1 to 2 hours until firm.,Slice into bars and store in an airtight container.