Preheat the oven to 425°F.
Place the Brussels sprouts and sweet potatoes in a large mixing bowl. Add 2 tablespoons of olive oil, the minced garlic, rosemary, paprika, salt, and pepper. Toss until the vegetables are evenly coated.
Spread the vegetables in a single layer on a large baking sheet. Roast for 15 minutes.
While the vegetables roast, pat the cod fillets dry and brush them with the remaining tablespoon of olive oil. Sprinkle with salt and pepper.
Remove the baking sheet from the oven and nestle the cod fillets among the vegetables. Return the sheet to the oven and roast for 12 to 15 minutes more, until the fish flakes easily with a fork and the vegetables are tender and browned at the edges.
Remove from the oven and serve immediately with lemon wedges and a sprinkle of fresh parsley.