01 - Preheat oven to 400°F and line a baking sheet with parchment paper or lightly grease it.
02 - Pat cod fillets dry with paper towels. Brush both sides with olive oil.
03 - Combine Cajun seasoning, smoked paprika, garlic powder, salt, and black pepper in a bowl. Sprinkle the mixture evenly on both sides of the fillets.
04 - Place cod fillets on the baking sheet and top each with a slice of lemon. Bake for 12 to 15 minutes, until flesh is opaque and flakes easily with a fork.
05 - While cod bakes, heat olive oil in a saucepan over medium heat. Add diced onion, carrot, and celery; sauté for 3 to 4 minutes until softened.
06 - Stir in minced garlic and cook for 1 minute. Add rice and dried thyme; toast for 1 to 2 minutes, stirring constantly.
07 - Pour in chicken broth or vegetable broth. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes.
08 - Stir in frozen peas, cover, and continue cooking for 5 minutes, until rice is tender and liquid is absorbed.
09 - Remove saucepan from heat. Fluff rice with a fork, mix in chopped parsley, and season with salt and pepper to taste.
10 - Spoon rice pilaf onto plates and top with baked Cajun cod fillets.