Head to Admin>Meals>Set up Meal Types and click on Add New to set up a Christmas Meal.
Select the year groups you wish have this meal available for, or you can set up an additional Christmas Meal for staff to select.
Then go to Admin>Meals>Set Meal Availability to assign the meal to the day it is available.
If you then go to Admin>Meals>Manage Student Lunches, select the date the meal is available, you can assign the Christmas meal by ticking in that meal choice column against each student who requires it.
Repeat this process in Admin>Meals>Manage Staff Lunches to assign the meal to staff.