Heat olive oil in a large pot over medium heat. Add chopped onions and sauté until translucent.
Stir in minced garlic and cook for another minute.
Add chopped cabbage, bell pepper, carrots, and celery to the pot. Cook for 5-7 minutes, stirring occasionally.
Pour in the chicken broth and diced tomatoes. Stir well to combine.
Add Cajun seasoning, salt, and black pepper. Stir to mix the spices evenly.
Bring the soup to a boil, then reduce heat to low and let it simmer for about 30 minutes, until the vegetables are tender.
Taste and adjust the seasoning if necessary. Serve hot.