I could just give you the answer, but ideally what you want to do is understand the process so you can do it for yourself. For something like this, which can be neatly divided into portions by cutting, it's simply a matter of looking at your raw ingredients and dividing by your portion size. Determining portion size gets a bit more confusing (which is likely what confused you) when dealing with things such as soups, stews and chili, where you've got all your food groups mixed into a large pot of something, and you can't slice it into neat little portions.
To walk you through this, in this recipe you're got 8 egg whites and 1 3/4 cups of raw pumpkin. The water, Splenda and flavorings are non-issues when it comes to figuring out portion size. To figure out portion sizes, whenever practical I'll try to base serving sizes upon the number of protein servings there are per recipe-- otherwise, figuring out portions of egg whites gets horribly confusing. In some recipes, you'll find there's a ton more carb than anything else, in which case you may have to figure things out in terms of the carb servings instead of protein.
In this recipe, you can see right off the bat that there are 4 (2 oz) servings of protein. Figuring out the carb isn't quite as tidy-- a glance tells you that there are more than 3 (1/2 cup) servings of carb in this; less than 4 servings. When faced with something like this, I'll actually break things down into tablespoons or even teaspoons to get an exact measurement. Just in case you don't know (and tattoo this information onto the back of your hand or inside your eyelids if it's new to you) there are 16 tablespoons in a cup, 3 teaspoons to a tablespoon. Your 1 3/4 cups of pumpkin translates to 28 tablespoons. Since we're working with 4 protein servings, we're going to try to divvy the pumpkin up also into 4 servings, so 28 divided by 4 equals 7. This means that in each of four servings you will get 2 oz protein, 7 tablespoons carb. Since there are 16 tablespoons in a cup, 8 tablespoons in a half cup, you'll be coming up 1 tablespoon shy of the 1/2 cup carb requirement with every 1/4 of this recipe you eat.
If your eyes are still rolling in opposite directions, drop me a PM with another recipe which confuses me and we'll work on it together. It's really important that you're clear on how the system works.