Preheat your oven to 200°C (400°F). While it heats, line a 9x13 inch baking dish with aluminium foil for effortless cleanup. You'll hear the foil crinkle as you press it into the corners.

Prepare the tomato-olive mixture. In a medium mixing bowl, combine the halved cherry tomatoes, chopped olives, sliced garlic, capers, dried oregano, smoked paprika, lemon zest, and half the olive oil. Stir everything together until the tomatoes are glossy and coated—you'll see the red juices starting to release.

Spread the mixture evenly across the bottom of the prepared baking dish. If using red onion, scatter the slices over the top now. The dish should look vibrant and colourful, with the tomatoes and olives scattered in a single layer.

Season the salmon fillets on both sides with salt and pepper. Place them skin-side down (if using skin-on fillets) on top of the tomato-olive mixture, leaving a little space between each piece so they cook evenly. Drizzle the remaining olive oil over the salmon.

Bake uncovered for 15–18 minutes. At the 15-minute mark, check for doneness: the salmon should be opaque and flake easily when gently pressed with a fork. The tomatoes will have softened and blistered, and you'll smell the garlic and oregano filling your kitchen.

Finish with lemon juice and fresh herbs. Remove the dish from the oven and squeeze the lemon juice evenly over the salmon and vegetables. Sprinkle the chopped parsley or basil on top. Let it rest for 2–3 minutes—you'll see the juices settle and the salmon firm up slightly as it rests.

Serve immediately by spooning the tomatoes, olives, and juices over each portion of salmon. The contrast between the flaky, tender fish and the rich, tangy sauce is exactly what you want.