I thought Nandos was British as it's been around here for a long time, but apparently it started in South africa. There is one where i live but i've never had one, only because i don't really eat out much. It is a healthier alternative to other eats cos they grill the chicken. One of my fav youtube vloggers ,Emily Hayward, was big into fitness and nutrition , despite having terminal cancer always made me laugh as it she always seemed to be having a nandos.
'Having a cheeky nandos ' is a widespread British idiom. But you could also say ' i went for a cheeky pint' or 'i had a cheeky burger'. It doesn't mean much prob just ;i know i shouldn't and don't tell anyone but i had a cheeky......'