There were rumours about the restaurants McDonald's cooking their fries in beef lard/oil if I remember correctly but apparently they stopped that a few years back. However some people still say it's best not to eat their food as they could still be doing so or even just using the same utensils for vegetarian foods which we can eat and for haram foods too.

Also a lot of other restaurants such as domino's pizza, subway, nandos and a lot of other takeaways – they have halal options, vegetarian options and also haram options. Can we still buy and eat from their food or should we avoid due to the possibility of cross contamination and foods being cooked in the same oven for example?

As far as McDonalds USA if you search their ingredients you will see they do coat their fries and hash browns in non halal animal fat. So this would make it unlawful for us.

As for other restaurants we can eat the halal and vegetarian options as long as we are not aware the food has been cross contaminated. Most of the times they would not do that because of threat of being sued by vegans or other religious groups who do not eat meat.

Allah knows best.

There were rumours about the restaurants McDonald's cooking their fries in beef lard/oil if I remember correctly but apparently they stopped that a few years back. However some people still say it's best not to eat their food as they could still be doing so or even just using the same utensils for vegetarian foods which we can eat and for haram foods too.

Also a lot of other restaurants such as domino's pizza, subway, nandos and a lot of other takeaways – they have halal options, vegetarian options and also haram options. Can we still buy and eat from their food or should we avoid due to the possibility of cross contamination and foods being cooked in the same oven for example?

It’s your responsibility to find out from your local restaurant to ascertain what is been speculated. Each restaurant differ depending on the locality. Kindly find out by either asking the management or people you trust.