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, oregano, salt, and black pepper until fully emulsified.
03 - Place trimmed asparagus in a single layer on one side of the prepared baking sheet. 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 tongs to ensure even coating.
05 - Nestle salmon fillets among the vegetables, skin-side down if applicable. Spoon the remaining marinade evenly over each fillet.
06 - Bake for 15-18 minutes, or until salmon flakes easily when tested with a fork and asparagus is tender-crisp.
07 - Remove from oven and sprinkle with fresh chopped parsley. Add an extra squeeze of fresh lemon juice before serving.