Cottage pie is filled with potatoes, beef and veggies so it would seem that it would check all the boxes of a gluten free recipe. However, you do want to be on the lookout for anything that might be used to thicken the gravy that covers the savory veggies. Flour does contain gluten and so if you are looking to produce a gluten-free meal, you can substitute it with cornstarch, arrow root or gluten-free flour.