When you sign up, you have the choice to flag any ingredients that contain gluten.
If you receive a recipe in your meal plan that has an ingredient that contains gluten, you will be alerted to that ingredient and reminded to use a gluten free alternative.
Your shopping list will also be tagged with any ingredients that contain gluten, so you can buy an alternative when you're at the shops.
Thankfully the choice of gluten free products is becoming more extensive all the time.