Heat the oven: Preheat to 400°F (200°C).
Lightly oil a large baking dish or sheet pan.
Toss the veggies: In the baking dish, combine tomatoes, red onion, bell pepper, olives, and capers. Add 2 tablespoons olive oil, half the garlic, oregano, thyme, red pepper flakes, a pinch of salt, and pepper. Toss to coat and spread evenly.
Roast the base: Bake the vegetables for 10–12 minutes until they start to soften and release juices.
This builds flavor and prevents undercooked veggies.
Season the fish: Pat fish dry. Rub with remaining 1 tablespoon olive oil, lemon zest, remaining garlic, salt, and pepper.
Nestle and bake: Remove the pan, push vegetables to make space, and lay the fish on top. Squeeze half the lemon over everything.
Finish cooking: Return to the oven and bake 8–12 minutes, depending on thickness.
The fish is done when it flakes easily and reaches an internal temp of 145°F (63°C).
Garnish and serve: Squeeze the remaining lemon, shower with chopped parsley, and taste for salt. Serve with your favorite side to soak up the pan juices.