For me, one of the benefits of drinking green smoothies is that when you use unprocessed, raw foods then your body knows exactly how to break down every item completely. Once you add protein powder to a smoothie, you are forcing your body to store waste and increasing digestive issues by adding sugar and chemicals that are not natural to your systems. If you eat a 400 calorie avocado, then your body can break it down completely and absorb its nutrients. A protein bar may have fewer calories and more protein but the body regards it very differently and some elements of the protein bar may end up floating around like styrofoam in your body. You don't have to worry about calories or read labels when you're eating whole, unprocessed foods! If the food is in its natural state, it will be much easier for you to make informed decisions about what you put into your body.
Okay...so my body can easily absorb and digest green smoothies, but am I getting any protein from drinking them? There are plenty of high-quality protein building blocks in greens and plant protein leads to long-lasting, slower-to build but slower-to-degenerate muscle mass. Gorillas eat plants all day and they don't seem to be lacking in muscle mass. It is much easier for the body to create protein from the assortment of individual amino acids found in greens rather than the already-combined long molecules of complex protein that comes from eating animal products. If you maintain a variety of greens in your diet, you will receive all essential amino acids in abundance. Also, getting your protein from plant sources may help decrease your risk of disease and make your body more alkaline.
So if you want to increase the amount of protein in your green smoothies, just pack in more spinach, kale, cucumber, avocados or any other greens. Try adding some chia seeds, a scoop of almond butter, bee pollen or whatever else you would like to experiment with in your recipes. As always, do whatever works for YOU. Everyone is different and you should keep experimenting and listen to your own body. There isn't one right answer. Since you are always learning and changing, you may have a different food philosophy today than you will a year from now. Stay open to the possibilities.