Preheat the oven to 325℉ or 165℃.

While the oven is heating, line the baking sheet with parchment paper.

Drizzle with olive oil.

Toss onion with olive oil, salt, and pepper. Lay on a baking sheet.

Place cleaned fish on the baking sheet.

Stuff each cavity with a lemon wedge, 1 rosemary sprig, and some red onion.

Mix white wine and lemon juice. Pour the mixture over the fish.

Sprinkle the fish with salt, pepper, and oregano.

Drizzle olive oil on top of everything.

Once the oven is preheated, put the fish in.

Bake the fish for about 25 minutes. Fish should be flaky and opaque

Remove the fish from the oven.

Remove the bones from the fish.

Serve fish with fresh lemon wedges and parsley.