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