You bet! In the Meal Selection area of your account, just select 'ADD EXTRA MEAL'. This will just affect the upcoming delivery, and your box will return to your regular number of meals after. The most recipes you can have depends on your box type:
Classic box: 8
Family box: 7
Veggie box: 5
To select your meals, click here.
Changes must be made before 11.59PM TUESDAY (Sydney time) for all states, the week before your next delivery.