PREP: Prepare the veggies (or buy pre-chopped veggies for an even quicker prep). Slice the celery into 1/4th-inch thick pieces. Very finely dice the onion. Cut the bell pepper into 1/4th-inch pieces. Finely mince the garlic. Trim excess fat from the chicken thighs.
CROCKPOT: Add everything to the slow cooker: the trimmed chicken thighs, sliced celery, diced onion, diced pepper, minced garlic, both cans of undrained stewed tomatoes, chicken stock, Cajun seasoning, ground cayenne pepper, and bay leaf. Season to taste with salt and pepper (I typically add 1/2 teaspoon seasoned salt and 1/4 teaspoon pepper). Stir everything together.
COOK: Cook on low for 5-8 hours or on high for 3-5 hours, until the chicken easily shreds. Every slow cooker cooks a bit differently so watch yours carefully! Avoid opening the slow cooker more than needed, as it takes a while for everything to return to temperature.
CHICKEN: Once everything is cooked, use tongs to remove the chicken thighs to a bowl. Use two forks to shred.
ROUX: About 30 minutes before serving, place a pot on the stovetop and heat the pot to medium-high heat. Add the butter and whisk until completely melted and frothy. Briskly whisk in the flour, 1 tablespoon at a time, adding slowly. Whisk until smooth in between each flour addition.
ROUX CONT.: Whisk constantly until a creamy mixture forms (if it clumps you'll need to start again). Lower the heat and allow to slightly thicken and then remove from heat. Carefully pour it into the slow cooker (it sizzles when added, so be careful!) Gently stir the roux into the chicken-veggie mixture.
FINISHING CROCKPOT: Add the chicken back into the slow cooker. Stir, taste and adjust the dish to personal preference, adding more salt and pepper as needed and/or additional Cajun seasoning. Remove the bay leaf and discard.
RICE: (you can use the same pot here as the roux to save on dishes!) Cook rice according to package directions or follow my foolproof method for cooking rice in a fraction of the time! See Note 2.
SERVING: Divide rice evenly among bowls. Spoon the slow cooker mixture on top and stir the two together. If desired, add some chopped green onions to each bowl. Enjoy!