01 - Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease a baking dish to prevent sticking.
02 - Carefully arrange the salmon fillets on the prepared baking sheet, ensuring each piece has sufficient space around it for even cooking.
03 - Generously spread 1 to 1.5 tablespoons of basil pesto over the top surface of each salmon fillet, coating them evenly.
04 - Scatter the halved cherry tomatoes and, if using, the thinly sliced red onion around the salmon fillets on the baking sheet.
05 - Drizzle olive oil over the scattered tomatoes and onions. Season the entire dish, including the salmon and vegetables, with sea salt and freshly ground black pepper.
06 - Bake for 15 to 20 minutes, or until the salmon flakes effortlessly with a fork and the tomatoes have softened. Note: Thicker fillets may require a slightly extended baking time.
07 - Remove the baked salmon from the oven and serve immediately, garnished with fresh lemon wedges for a bright finish.