Preheat your oven to 400°F and grab your favorite baking dish.
Place the fish fillets in the dish, giving them room to breathe—nobody likes crowded fish.
Scatter the tomatoes, red onion, garlic, and olives over and around the fish like confetti.
Drizzle everything with olive oil, sprinkle on the oregano, salt, and pepper. Then lay those lemon slices across the top like it’s getting ready for the spa.
Bake for about 15–20 minutes, or until the fish flakes easily with a fork.
Top with fresh parsley, serve hot, and pretend you’re on vacation. No passport required.