This tuna salad keeps in the fridge for up to one week. When you're ready to enjoy it for lunch, spread the tuna salad in pita pockets and add lettuce and tomato.
Mix first 4 ingredients in a medium bowl until well combined. Season with salt and pepper. Place 1/2 tuna salad in an airtight container; cover and chill (will keep for up to a week).
Spread remaining salad in pita pockets. Carefully push in tomato and lettuce.