Cook sausage in a Dutch oven over medium-high heat, breaking it up into small pieces with a wooden spoon, until cooked through, about 5 minutes. Transfer to a medium bowl lined with paper towels.
Return the pan to medium-high heat and add oil. Add onion and cook, stirring often, until translucent, about 2 minutes. Add garlic and Cajun seasoning and cook, stirring often, until fragrant, about 30 seconds. Add flour and cook, stirring to coat the vegetables, until the flour browns, about 1 minute. Add tomatoes and cook, stirring occasionally, until they begin to release their juices, about 2 minutes. Stir in broth, cover, increase heat to high and bring to a boil.
Return the sausage to the pan, along with okra and rice; reduce the heat to a simmer. Cook until the okra is heated through and the rice is tender, about 10 minutes. Serve sprinkled with sliced scallions, if using.