Place the brown rice in a saucepan with 1/2 cup water. Bring to a boil, reduce the heat to low and simmer, covered, until almost all the water is absorbed, approximately 40 minutes.
In a pot with a steamer basket, bring a small amount of water to a boil. Add the kale to the basket and steam for about 10 minutes, making sure to add more water if needed; set aside. Add the broccoli to the steamer basket and steam for about 6 minutes; set aside. Add the sweet potatoes and steam until just tender, 10 to 20 minutes. (Alternatively, if space allows, steam the vegetables together, making sure to remove each type as it cooks.)
Place the rice, kale, broccoli and sweet potatoes into different sections of a compartmentalized lunch box. Cut the egg in slices, if desired, and place in another section. Finally, add the avocado.