Beef would make it a meat protein product and therefore not on the recommended list for the diet.
You could look at the legumes, (beans), for another protein source, or go with pea protein powder if you want to use it in smoothies and shakes.
The following is quoted from here
Here is a list of 10 high-protein vegetables that you can add into your life for more energy and to help create vibrant health naturally.
Not only are peas one of my favorite kitchen additions, but they are an excellent source of protein. Peas can be enjoyed fresh or frozen and have some of the highest protein available of any vegetable. So, next time you are looking for a little protein boost, remember to add in a handful of peas to your meal.
You might already know spinach as a popular "super food", but now you can eat it knowing that it is also a great source of protein, too. This vegetable is loaded with vitamins, minerals and antioxidants and within that deep dark green color is also plenty of protein.
Truly one of the best greens and vegetable choices out there, kale is the definition of a super food. Make it into a salad, add it to soup or casserole, or blend a handful into a green smoothie, knowing that you are getting your protein.
As well as protein, broccoli is also high in fiber, antioxidants and minerals. With a broad range of vitamins on offer, you can use cooked or raw broccoli as a main menu item. Eat broccoli in salads, soups, or simply steamed by itself with a squeeze of fresh lemon juice.
There are so many different varieties of fresh sprouts available and the thing I love about them is that they are living until you pick them. (You can't get any fresher than that.) Sprouts make a healthy addition to sandwiches, salads and soups. Try mixing the various kinds of sprouts that are available, as the different varieties are all delicious.
With a firm texture and immune boosting properties, especially the cordycep, reishi and maitake varieties, mushrooms make a tasty, nutritious and filling main meal. I like to cook them under a hot grill with a drizzle of olive oil. When they are almost done, simply top them with a little freshly chopped garlic and parsley and then bake them a little longer (to cook the garlic). Serve them with freshly scrambled organic eggs for a healthy weekend brunch.
7. Brussel Sprouts
This cruciferous vegetable is not only high in protein, but also fiber. I remember as a little girl not being very keen on brussel sprouts. Fortunately, my taste buds have evolved! Try roasting them in a baking tray with a drizzle of oil and a dash of sea salt for a delicious variation.
You can eat artichokes in many different ways including blended, steamed or roasted. They are so delicious and filling (thanks to the high protein) that you may very well may make them the main part of your meal, as happened in the ancient Jewish Ghettos in Rome many years ago!
Not only are asparagus high in protein, but they also assist your body with detoxification. Asparagus are also high in fiber, which fills you up and leaves you feeling satisfied and satiated after eating.
In addition to its high fiber content, a serving of corn packs a solid protein punch. Best eaten fresh from the cob, you can also get the benefits off-season through frozen or canned kernels.