01 - Preheat the oven to 400°F. Line a baking dish with parchment paper or lightly grease with olive oil.
02 - Place the haddock fillets in the prepared baking dish in a single layer.
03 - In a small bowl, whisk together the olive oil, lemon zest, lemon juice, capers, minced garlic, salt, and black pepper.
04 - Pour the marinade evenly over the haddock fillets.
05 - Sprinkle the chopped parsley over the fish.
06 - Arrange lemon slices on top of the fillets.
07 - Bake for 18–20 minutes, or until the fish is opaque and flakes easily with a fork.
08 - Serve immediately, garnished with extra parsley if desired.