Sautee onions, celery and peppers in olive oil until soft, approximately 5-7 minutes. Add garlic and set vegetables aside. Melt butter in a stock pot over medium heat. Add flour and stir continuously to make a roux. Cook the roux over medium heat until the consistency resembles peanut butter, approximately 5 minutes. Add the sautéed onions, peppers and celery to the roux, stirring to coat the vegetables. Add the diced tomatoes, seasonings and bay leaves along with the seafood stock and bring the mixture to a boil. Reduce heat and simmer for 40-45 minutes, stirring occasionally. Add the shrimp and cook for an additional 5-7 minutes and then stir in the chopped parsley. Serve immediately over cooked long grain white rice.