Heat a large pot over medium heat and add the sliced sausage. Cook for 5 minutes until the edges brown and some fat renders out.
Add the onion, green bell pepper, and celery to the pot. Stir and cook for 4 minutes until the vegetables soften. Stir in the garlic and cook for 1 minute more.
Add the rice, diced tomatoes with their juice, chicken broth, and Cajun seasoning. Stir to combine and bring the mixture to a simmer. Cover the pot, reduce the heat to low, and cook for 20 minutes until the rice is tender and most of the liquid is absorbed.
Scatter the shrimp over the top of the rice. Cover again and cook for 5 minutes until the shrimp turn pink and opaque. Remove the pot from the heat and let it rest for 3 minutes. Stir gently, taste, and add salt or black pepper if needed. Sprinkle the green onions over the top before serving.