You guess based on the ingredients. I eat ethiopian food ocassionally and I found calories for injera (which is the bread) but couldn't find calories for the other stuff. But I knew it was lentils, greens, potatoes, carrots, etc and also some oil so I estimated as best I could. I did search a bit online though for ethiopian food and calories as well.
Here are some sites that I found in searching for meat pie/sfiha/safiha
http://www.recipezaar.com/Sfiha-Lebanese-Pie-263613 (recipe has some calories listed)
http://members.fortunecity.com/nbassaf/calories.html (lebanese food calories)
Oh and as always, recipes can vary so it is just an estimate but it may be a decent starting point if nothing else.