01 - Preheat oven to 400°F and line a baking tray with parchment paper or lightly oil a large baking dish.
02 - Rinse the sea bass under cold water and pat dry thoroughly with paper towels.
03 - Make 2–3 diagonal cuts on each side of the fish’s skin using a sharp knife to allow even cooking and flavor infusion.
04 - Rub the entire fish, inside and out, with olive oil, then season evenly with sea salt and freshly ground black pepper.
05 - Fill the fish cavity with lemon slices, garlic, fresh thyme, and rosemary sprigs for aromatic flavor.
06 - Spread red onion slices evenly on the baking tray and place the stuffed sea bass on top.
07 - Bake in the preheated oven for 20 to 25 minutes, or until the flesh turns opaque and flakes easily with a fork.
08 - Transfer the fish to a serving platter and garnish with chopped fresh parsley and lemon wedges, if desired. Serve immediately.