Step 1
Place chicken thighs in a large resealable bag; pour in blue cheese dressing. Coat chicken with dressing squeeze out excess air and seal the bag. Marinate in the refrigerator for 4 hours to overnight.
Step 2
Preheat oven to 420 degrees F (216 degrees C). Spray a 9x13-inch baking dish with cooking spray.
Step 3
Heat 2 tablespoons olive oil in a skillet over medium heat; cook and stir celery in the hot oil for 1 minute. Add onion; cook and stir until onion is glossy and softened about 5 minutes. Stir in garlic; cook for 30 seconds. Transfer onion mixture to the prepared baking dish; return skillet to burner.
Step 4
Pour remaining 1 tablespoon olive oil into the skillet; cook and stir rice in the hot oil until fragrant 2 to 3 minutes.
Step 5
Mix chicken broth rice and vinegar into the onion mixture in the baking dish. Remove chicken from marinade and arrange in the baking dish creating 2 rows of chicken thighs side by side. Discard remaining marinade. Sprinkle each chicken thigh with Cajun seasoning. Coat chicken thighs with 1 cup panko crumbs. Cover baking dish with aluminum foil.
Step 6
Bake in the preheated oven for 35 minutes. Remove aluminum foil from dish. Mince the reserved celery leaves. Sprinkle chicken thighs with remaining 1/2 cup panko crumbs and Parmesan-Romano cheese; sprinkle minced celery leaves over chicken.
Step 7
Continue to bake chicken until no longer pink at the bone and the juices run clear about 10 more minutes. An instant-read thermometer inserted near the bone should read 165 degrees F (74 degrees C).
Step 8
Turn on the oven's broiler and broil chicken until browned and crisp 1 to 3 minutes. Remove from oven and let cool for 10 minutes before serving.