This article provides a nice summary of five key nutrients needed and how to get them including protein, omega-3s, calcium, iron, and vitamin B12. Lately my source for B12 has been nutritional yeast blended into a morning smoothie. In the past, it has come from fortified soy-milk.
My protein requirement comes from tofu, lentils, black beans, quinoa, and mushrooms. I also eat plenty of nuts such as pistachios and almonds. For omega-3s, I add oils to my smoothies such as flaxseed oil and hemp oil and I also put in chia seeds which I buy in bulk from the supermarket. I get iron from a variety of foods but a lot from lentils and leafy greens. Lastly, my calcium comes from fortified tofu, leafy greens, and coconut milk.
It's important to eat a wide variety of plant-based foods since they will all contribute in some way to a balanced and healthy body.