Pat salmon dry; add 1/2 teaspoon salt and pepper. Heat oil in 12-inch nonstick or well-seasoned skillet over medium-high.
Arrange in one layer; cook undisturbed 3 to 4 minutes. Carefully turn; cook 1 to 2 minutes more until thickest pieces 145°F. Transfer to clean plate.
Add asparagus, water, and remaining salt. Cover; steam over medium 3 to 4 minutes until crisp-tender. Uncover; evaporate water 1 minute.
Reduce to low; stir butter and garlic around asparagus 30 to 45 seconds. Add lemon juice and zest.
Gently return salmon; warm 1 minute, spooning lemon butter over without breaking fish. Divide evenly with asparagus among 4 plates.