Preheat the oven to 200°C (180°C fan). While it's heating, line a large baking dish with aluminium foil. This isn't just for easy cleaning - the foil helps trap steam, keeping the cod tender and the green beans vibrant.

Prepare the lemon-garlic butter. In a small mixing bowl, combine the melted butter, minced garlic, lemon juice, lemon zest, smoked paprika, salt, and pepper. Whisk until everything is well incorporated. The aroma of garlic and lemon should hit you immediately - that's how you know it's ready.

Toss the green beans with olive oil. Place the trimmed green beans in the baking dish, drizzle with olive oil, and sprinkle with a pinch of salt. Use your hands to coat them evenly. The beans should look glossy and lightly coated, not dripping.

Arrange the cod fillets on top of the beans. Pat the cod dry with kitchen paper - this step is crucial for the sauce to cling properly. Place the fillets skin-side down (if they have skin) directly onto the green beans. You'll hear a slight sizzle if the dish is hot from the oven preheating.

Pour the lemon-garlic butter over the cod. Spoon the mixture evenly over each fillet, letting it drip down onto the beans below. The sauce should pool slightly around the fish, creating a shallow bath that will keep everything moist during baking.

Bake uncovered for 18-22 minutes. The cod is done when it flakes easily with a fork and the centre is opaque, not translucent. The green beans should be tender-crisp - they'll have a bright green colour and yield slightly when pierced with a knife. If you inserted a thermometer, the cod should read 63°C.

Rest for 2 minutes before serving. Remove the dish from the oven and let it sit on the counter. This resting period allows the juices to redistribute, so your cod stays moist rather than weeping onto the plate. Garnish with fresh parsley and capers if using.