Don't know the calories!

I make most of my food myself and can therefore weigh and scale accurately. I don't eat that much in restaurants, so it's not a big issue.

But I have a local lunch place which makes salads and I stop by there after the gym sometimes.

My favourite is this:
lettoslo.no/content/uploads/2014/10/Salat_Chevre-830x930.jpg

It's got goat cheese, beets, walnuts, lenses, apples and I use a spinach base.

I know the goat cheese and walnuts are high calorie, but I have no idea what amount to measure! It's all blended when I get it, so hard to measure.

What would your idea of calories be for something like this? How do you determine when you don't know?