There are few restaurants in New Zealand that serves Halal food, and even a few places that sell raw Halal food. In larger cities, such as Auckland and Wellington, there are quite a number of Halal Malaysia Restaurants, Indian Restaurants and Kebab stands. In smaller towns, it is unlikely that there will be such shops and restaurants.
In the cities, there are specialized shops that sell Halal foodstuff, Asian cuisine, etc. I have been to a number of Asian supermarkets around, and some of them do sell things like Sambal chilli and Halal Indomie Mee Goreng. In fact, the local supermarket chains also carry various Halal certified foodstuff, especially if there is a significant number of Muslims in the area.
One of my fave eating-places is Nando's, which happens to serve only chicken. Since the first time I went there was with my friends from Dubai, I am guessing that it is Halal. The good news is – there are heaps of branches located all around in major cities. In fact, there are more than 15 outlets in Auckland alone.
Another Halal restaurant I was to is Rasa Malaysian & South Indian Restaurant in downtown Wellington. To be honest, I only was there once, and it did not leave me a deep impression. The food was not bad or what, it was okay, just not that great to keep me wanting to go back.
My Muslim friends also greeted me to some Kebab Restaurants. The one I frequent the most is probably Jabies Doner Kebab at the town Bulls. It is so close to Palmerston North, and sometimes we just drive over to eat Kebab. We pass by quite often when we drive up North, as this is one of the places where we can turn to State Highway 1.
If you need to find where the Halal Restaurants and eating-places, most I-Site visitor centers will be able to provide you some recommendations. But I strongly recommend you to bring a few packs of instant noodles along, just in case you decide to stay in a smaller town for a night or so.