It's a SALAD.... I don't really count leafy greens and raw veg. I just limit my portions of starchy veg and tubers.
The best way to get a feel for estimating is to spend time actually looking up the nutrition amounts for the ingredients you are going to use and MEASURING them.
It's kind of inconvenient when you are in a rush, but it can be done ahead. Like putting 2-3 cups of salad greens into bags and so forth for other ingredients such as red peppers. And after a while you'll know pretty much at a glance what you are tossing onto your plate without measuring anything.