Heat oven to 425°. Pulse 2 3/4-inch-thick slices country-style bread, crusts removed in a food processor until coarse crumbs form. Heat 2 Tbsp. oil in a large ovenproof skillet over medium-high heat. Add breadcrumbs. Cook, stirring often, until golden and crisp, about 3 minutes; season with salt and pepper. Transfer mixture to a bowl, add 1 Tbsp. chopped fresh flat-leaf parsley and 1 Tbsp. fresh oregano leaves; toss to combine. Wipe out skillet. Heat 1 Tbsp. oil in same skillet over medium-high heat. Add 1 small shallot, thinly sliced and 2 oz. smoked Spanish chorizo, halved, thinly sliced and cook, stirring often, until chorizo is just crisp, about 2 minutes. Transfer to a bowl and mix in 2 Tbsp. Sherry or red wine vinegar; season with salt and pepper. Wipe out skillet. Heat remaining 1 Tbsp. oil in same skillet over medium-high heat. Season 4 6-oz. pieces skinless cod or halibut fillets with salt and pepper and cook until bottom side begins to turn opaque, about 3 minutes. Transfer skillet to oven and roast until fish is cooked through, about 5 minutes longer. Serve cod topped with chorizo mixture and toasted breadcrumbs.