Preheat oven to 400°F (200°C) and grease a large rimmed baking sheet.
In a large bowl, toss the sliced potatoes with 1.5 tablespoons of olive oil, 0.5 teaspoon salt, and 0.25 teaspoon pepper.
Spread potatoes in a single layer on the baking sheet and roast for 20 minutes until tender.
Remove the sheet pan from the oven; move potatoes to the sides and add chickpeas and minced garlic to the center, tossing slightly with the residual oil.
Season cod fillets with the remaining salt, pepper, and smoked paprika.
Place the cod fillets on top of the chickpea and potato mixture.
Drizzle the remaining 1.5 tablespoons of olive oil over the fish and top with lemon slices and dried oregano.
Return to the oven and bake for 12 to 15 minutes until the cod is opaque and flakes easily with a fork.
Garnish with fresh chopped parsley and serve immediately.