I have tried searching the internets for this answer...but no dice. Do you measure food BEFORE or AFTER it is cooked? I tested this with some ground turkey, and it was 4oz pre cooking, and then it shrunk to around 3 after cooking.
This is a GREAT question. I see a lot of people get confused over this.
The short answer is it depends! Either works as long as you use the correct nutritional info for what you have choosen.
For example, you mentioned ground turkey. I weigh it raw, I weigh all my meats raw. Then when I look up the nutritional information for it I make sure I'm looking at the raw values. Take a look at NutritionData's entries for ground turkey, they give you the choice between raw and cooked.
My advice, you have to find what works for you. Some like to weigh post cooking I tend to weigh everything before cooking in it's raw state. So when I give ounces or grams in my ingredient lists it's raw and I use those figures to calculate the nutritional info for the dish.
But it really comes down to personal preference.
I should add, I think most recommendations in serving size are precooked.
I hope that helps a little.
P.S. How do you guys weigh your food?