Prep all ingredients as listed above.
Sauté Aromatics: In a small skillet, heat olive oil over medium heat. Add onion, bell pepper, celery, and garlic. Sauté 3–4 minutes until softened.
Combine Ingredients in Slow Cooker: Transfer sautéed vegetables to the slow cooker. Add chicken, sausage, diced tomatoes (with juice), chicken broth, Cajun seasoning, thyme, paprika, cayenne pepper, salt, black pepper.
Cook Gumbo: Cover and cook on low for 6 - 8 hours (or on high for 4 hours), until chicken is tender and flavors have melded together.
Cook Rice: Prepare rice according to package directions. Fluff with a fork and keep warm.
Add Shrimp: Stir the shrimp into the slow cooker and cook for an additional 20 - 30 minutes until shrimp reach an internal temperature of 120F / 48C.
Finish and Serve: Taste and adjust seasoning if needed. Stir in lemon juice for brightness if desired. Serve gumbo with rice, garnished with chopped scallions and lemon sparkling water.