Pat the salmon fillets dry with a paper towel. In a small bowl, mix the olive oil, garlic powder, smoked paprika, dried herbs, salt, and pepper. Brush the mixture over the salmon fillets and toss the trimmed asparagus in the remaining oil and spices until evenly coated.
Preheat your air fryer to 400°F (200°C) for 3 minutes. Place the salmon fillets in the center of the air fryer basket. Arrange the asparagus around the salmon in a single layer. If your basket is small, you may need to tuck the asparagus slightly, but try not to overlap them too much for the best texture.
Slide the basket into the air fryer and cook at 400°F (200°C) for 10 to 12 minutes. The salmon is done when it reaches an internal temperature of 145°F and flakes easily with a fork. The asparagus should be tender and slightly charred at the tips.
Carefully remove the salmon and asparagus from the basket. Squeeze fresh lemon juice over everything and garnish with extra lemon slices. Let the salmon rest for 2 minutes before serving to ensure it stays juicy.