In a large saucepan, heat the olive oil over medium heat. Add the diced onion, bell pepper, and celery. Sauté for about 5 minutes until the vegetables are softened.

Stir in the minced garlic and Cajun seasoning. Cook for an additional minute until fragrant.

Add the rice to the saucepan, stirring to coat the rice with the oil and vegetables.

Pour in the chicken broth, salt, and black pepper. Stir to combine everything evenly.

Bring the mixture to a boil, then reduce the heat to low. Cover the saucepan and let it simmer for 15-20 minutes, or until the rice is cooked and the liquid is absorbed.

Once the rice is done, remove it from heat and let it sit covered for 5 minutes before fluffing it with a fork.

Serve the Cajun rice warm, garnished with sliced green onions.