Preheat oven to 400 degrees.
Place potatoes in a medium saucepan; cover with water and cook over high heat for 15 minutes or until fork-tender; drain.
Cut potatoes into 1-inch slices then spread them on a baking sheet coated with 1 tablespoon of olive oil. Arrange cod fillets on top.
In a medium bowl, combine remaining 3 tablespoons of olive oil, the garlic, lemon juice and capers; drizzle mixture over fish and season with salt and pepper.
Bake for 10 to 12 minutes or until fish flakes easily when tested with a fork.
To serve, garnish fish with chopped parsley.