Place a large pot over medium heat and add the sliced sausage. Cook for 5 to 6 minutes, stirring occasionally, until the edges brown and some fat renders out.
Add the onion, green bell pepper, and celery to the pot. Cook for 4 minutes until the vegetables begin to soften.
Stir in the garlic and Cajun seasoning and cook for 1 minute until fragrant.
Pour in the diced tomatoes with their juices, then add the rice and chicken broth. Stir once to combine everything evenly.
Bring the mixture to a boil, then reduce the heat to low, cover the pot, and simmer for 20 minutes without lifting the lid.
Remove the pot from the heat and let it sit covered for 5 minutes. Fluff the rice gently with a fork, then sprinkle the green onions over the top before serving.