In a medium saucepan, combine brown rice and water; bring to a boil, then reduce heat to low, cover, and simmer for 35 minutes until water is absorbed and grains are tender.
Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).
On a large rimmed sheet pan, toss the cubed chicken and sweet potatoes with 2 tablespoons of olive oil, garlic powder, smoked paprika, salt, and pepper until evenly coated.
Spread the chicken and sweet potatoes in a single layer and roast for 20 to 25 minutes until the chicken reaches an internal temperature of 165 degrees Fahrenheit and the sweet potatoes are fork-tender.
While the chicken roasts, place the chopped kale in a large mixing bowl with the remaining 1 tablespoon of olive oil and the lemon juice; massage the kale with your hands for 2 to 3 minutes until the leaves are softened and dark green.
To assemble, divide the cooked brown rice into four bowls, then top with equal portions of the roasted chicken, sweet potatoes, and massaged kale.