01 - Preheat oven to 400°F. Line a large rimmed baking sheet with parchment paper or lightly grease with olive oil.
02 - In a small mixing bowl, whisk together olive oil, lemon zest, lemon juice, minced garlic, dried oregano, salt, and black pepper until well combined.
03 - Spread trimmed asparagus in a single layer on one side of the prepared sheet pan. Arrange halved cherry tomatoes and sliced red onion on the remaining space.
04 - Drizzle half of the lemon herb mixture over the vegetables. Toss gently with your hands or tongs to ensure even coating.
05 - Nestle salmon fillets among the vegetables, ensuring they are not overlapping. Spoon the remaining marinade evenly over each salmon fillet.
06 - Bake for 15 to 18 minutes, or until salmon flakes easily with a fork and asparagus is tender-crisp. Cooking time may vary slightly based on salmon thickness.
07 - Remove from oven. Sprinkle fresh chopped parsley over the entire dish and add an extra squeeze of fresh lemon juice before serving warm.