Melt the butter in a large, heavy bottomed pot set over medium-high heat. Whisk in the flour and cook, stirring constantly to make a light-to-medium brown roux (about the color of peanut butter or a little lighter). Immediately add the chopped onion, bell pepper and celery. Reduce the heat to medium and cook, stirring often, for 10 minutes. Stir in the garlic, three peppers, salt and paprika; cook 1 minute. Add the chicken stock and stir to mix. Bring the mixture to a boil, stirring often.
Transfer the contents of the pot to the slow cooker and add the cubed chicken. Stir to mix, cover and cook on HIGH for 3 hours or LOW for 6 hours. Stir in the sliced green onions and chopped parsley, adjust seasonings and cook, covered for an additional 5-10 minutes.