Soak the beans in enough water to cover 8 – 24 hours. Reserve the seasoning packet. Rinse and drain the beans, put in a large soup pan with 10 cups water, the reserved seasoning packet and the granulated garlic. Bring to a boil, reduce heat and simmer, covered, for 1¼ hours.
While the beans are simmering, heat the oil in a skillet over medium heat. Whisk in the sweet rice flour and cook until it becomes deeply browned, stirring occasionally, about 20 minutes. Stir the onion and celery into the flour mixture; it will become very thick. Stir the flour mixture into the beans after they have simmered for 1¼ hours.
Heat the remaining tablespoon of oil in a skillet and cook the bells peppers until they start to soften and brown, about 5 minutes. Add to the beans. Add the okra to the skillet and cook, stirring often, until they start to brown, about 5 minutes. Stir into the beans. Let the beans simmer for another ½ hour to thicken.
Adjust seasoning with additional salt and pepper if needed and a few (or more) dashes of Tabasco.
Serve the gumbo in a bowl over hot, cooked rice and garnish with chopped scallions.