1. Adjust rack in lower third of oven. Heat oven to 450 degrees F.
2. Arrange potatoes, sweet peppers and garlic on a jelly-roll pan. Toss with 2 tablespoons oil, 1/4 teaspoon salt and 1/4 teaspoon pepper. Roast about 15 to 20 minutes, until potatoes are fork-tender and peppers are golden. Transfer peppers and garlic to a cutting board. Squeeze garlic out of skin; finely chop garlic and peppers. Toss potatoes with 1 tablespoon oil. Cover with foil to keep warm.
3. Meanwhile, rinse cod fillets and pat dry with paper towels. Sprinkle remaining 3/4 teaspoon salt and 1/4 teaspoon pepper on both sides of each fillet. Heat remaining 1 tablespoon oil in a large ovenproof nonstick skillet over medium-high heat. Add cod, skin side down, and cook 2 to 3 minutes, until skin is crisp and golden brown. Arrange rosemary on top of fish. Transfer skillet to oven and roast 3 minutes. Turn fish; roast 3 minutes more, until fish is opaque and cooked through.
4. Spoon pepper mixture evenly on top of each fillet and serve with potatoes. Makes 4 servings.