Preheat the oven to 425℉. Grease your casserole dish with olive oil or butter and set aside. You can also line the bottom with parchment paper to prevent sticking, but I don't think that it's necessary.
In a medium sized pot, heat the vegetable stock, soy milk, and nutrititional yeast until it comes to a low boil.
Meanwhile, add the yellow onion, garlic, brown rice, chickpeas, sundried tomatoes, celery, dried oregano, salt and pepper to the casserole dish. Stir well to combine.
Once the vegetable stock, soy milk, and nutritional yeast mixture has come to a low boil, remove from the heat and pour over the top of the dry ingredients in the casserole dish. Stir well to combine all ingredients, making sure that the rice is completely submerged. If you don't do this, some of the rice might not cook fully.
Cover with tinfoil, then bake in the oven for 30 minutes. After 30 minutes has passed, remove from the oven, uncover and add the frozen broccoli florets. It's okay if they're not fully submerged in the liquid.
Replace the tinfoil and bake the casserole for another 25 minutes, or until the edges are lightly golden brown and the rice is fully cooked. Remove from the oven, garnish with the lemon juice and parsley and enjoy!