4 teaspoons extra-virgin olive oil, divided
1 medium onion, very thinly sliced
1/2 cup dry white wine
8 ounces Pacific cod (see Note) or tilapia, cut into 2 pieces
1 teaspoon chopped fresh thyme or 1/4 teaspoon dried
1/4 teaspoon kosher salt
1/4 teaspoon freshly ground pepper
3/4 cup finely chopped whole-wheat country bread (about 1 slice)
1/4 teaspoon paprika
1/4 teaspoon garlic powder
1/2 cup finely shredded Gruyère or Swiss cheese
Preheat oven to 400°F.
Heat 2 teaspoons oil in a medium ovenproof skillet over medium-high heat. Add onion and cook, stirring often, until just starting to soften, 4 to 6 minutes. Add wine, increase heat to high and cook, stirring often, until the wine is slightly reduced, 2 to 4 minutes.
Place fish on top of the onion and sprinkle with thyme, salt and pepper. Cover the pan tightly with foil; transfer to the oven and bake for 12 minutes.
Toss the bread with the remaining 2 teaspoons oil, paprika and garlic powder in a small bowl. Uncover the fish; top with the bread mixture and cheese. Bake, uncovered, until the fish is just cooked through, 8 to 10 minutes.