It's fine. It's sociable and a way of bonding with his squad.
But what you could do is teach him to make a burger, and get him to invite all his mates home to eat them.
Once he has got the hang of it he can get a few of them to help him out the day before to prep it all, so when they are tired and get back all they have to is cook everything.
Or if you are feeling generous, you can do the cooking.
A burger is just a meat omelette; quality minced beef, garlic, chilli, eggs, cayenne pepper, black pepper & salt.
Gruyere & Emmental cheese, mayo, ketchup & fresh rolls.
Chips cooked in olive oil, get one of those 3 litre tubs from Asda for a tenner.
On a hot day bbq them or cook them on an iron skillet.
They will soon get bored of MacDonald's!