Interesting, I just typed "green peas" into Google, and what it shows me in the sidebar shows 5g of protein per 100g, which isn't very high at all. But split peas seem to have only 8.3g per 100g which isn't much higher - I guess a lot of the pea is removed in making the protein from them.

Mostly the water is removed. Fresh green peas are 80% water by weight, similar to most fresh produce. And of course there's a lot of carbs.

I find the protein to calorie ratio is more useful.