There's a couple things you want to watch out for. Protein is the obvious one but there's others. Dietary B12 only comes from meat but you can easily supplement with vitamins. Iron from plants is less bioavailable but can also be supplemented. Other than that, the usual trail mix of seeds and nuts is really helpful for getting enough protein and essential fatty acids. The big divide in this category is Omega 6 vs Omega 3 fatty acids. Most give O6 (peanuts, sunflower seeds, hazlenuts, etc), while only a few give O3 (ground flax seeds, hemp hearts, chia seeds). For me a tablespoon or so of hemp for O3 plus a good assortment of the O6 varieties seems to do the trick. Another thing to keep in mind is that a lot have people have decided that grains = bad, but as a veggie you'll likely get most of your calories, protein, and water soluble vitamins from them. So choose ones with more concentrated nutrients and eat a variety of them (wheat is king, oats and potatoes are good, rice is poverty tier). One last tip, it's really easy to go overboard on vegetables that are heavy in oil-soluble vitamins, like carrots and spinach, because they tend to be cheap and versatile. The problem is that oil-soluble nutrients build up in your system and can become toxic at high enough levels. So don't just eat a ton of carrots for your vegetables, moderation is key. If you have any questions about what's the best bang for the buck, I highly recommend the site
https://nutritiondata.self.com/. It pulls the data from the Standard Reference USDA nutrition database, which is by far the most complete, detailed, and well-sourced nutrition reference I've ever found.
