What to do when he only wants 1 specific thing to eat?

Noona • 🇱🇧💍👶🏻👶🏻🇬🇧

So my son has been refusing dinner regardless of what I try to give him unless it is either porridge, weetabix, or cerelac. He will keep crying until he gets one of those options offered to him. I've tried so much and just don't know what to do to break that habit as he's not getting much nutrition from any of those options. I don't want him going to bed hungry so I feel like I have no other choice.. what do I do?