Can I heat up overnight oats
Soaking oats in milk overnight makes for very good porridge, with little effort in the morning as you just have to heat it through. So you're very close to something standard. 

The golden syrup and fruit won't come to any harm from being soaked then heated, though you could equally stir them, or just the fruit, in at the end.

The only thing needing a bit of care is the yoghurt. It's probably better to start with it mixed in rather than stir it into hot porridge, as adding yoghurt to hot food causes it to separate, as does overheating it. So assuming you put your entire soaked breakfast into the microwave, you should heat it fairly gently, perhaps 1 minute on high, stir, 30 seconds on high, stir and see if it's hot enough (with further 30s bursts until it is). If your microwave is very powerful or uneven, the first step will need to be shorter. You may find with testing that you can just blast it until it's hot; this partly depends how much yoghurt there is in relation to the amount of milk.