Side quests in Paper Mario: The Thousand-Year Door unlock as you progress through the story, so you'll want to swing by Rogueport East and check the Trouble Center. If you're aiming to 100% the cookbook, then you'll need to complete the "Security code..." Trouble. The side quest can be tedious as it requires a lot of backtracking to each area you've unlocked. Despite this, the reward for "Security code..." can potentially unlock various recipes that can help you in battle.