Did you work out the total carbs for the meal? That is usually a good place to start. If the food is not in a packet with a nutrition label you can usually find the carb content from a supermarket website such as this (baby new potatoes)
https://www.tesco.com/groceries/en-...gclsrc=aw.ds&dclid=COnM04fU1tsCFc_gGwodtGMKWg
It looks like the new pots and the red onion were the problem. You could try this again without the red onion and see what happens. Or miss out/reduce the spuds. Either one (or both) of these could be your nemesis. Also, did you have any thing else, such as tomatoes, a salad dressing or similar? I don't see any fat in that meal either.