Bring 1 1/2 cups water to a boil in a saucepan; stir in brown rice. Reduce heat to medium-low, cover, and simmer until rice tender and liquid has been absorbed, 40 to 50 minutes. Set aside.

Cook and stir turkey in a skillet over medium heat until renders some of fat, 2 to 3 minutes; stir in bell pepper, onion, and minced garlic. Continue cooking and stirring until turkey crumbly and no longer pink, and vegetables tender, 5 to 8 minutes more. Drain excess grease, if necessary. Stir in cooked brown rice, 1/3 cup water, Cajun seasoning, garlic powder, celery flakes, and black pepper.

Bring rice mixture to a simmer; cook until liquid is absorbed, about 10 minutes. Season with salt and black pepper.