Step 1

Pat 1 1/2 pounds boneless, skinless chicken pieces dry with paper towels. Season all over with 3/4 teaspoon of the kosher salt and 1/4 teaspoon black pepper.

Step 2

Heat 1 tablespoon of the olive oil in a 12-inch or larger cast-iron or stainless steel skillet over medium heat until shimmering. Add half of the chicken in a single layer. Cook until golden-brown on the bottom and the chicken easily releases from the pan, 3 to 5 minutes. Flip and cook until golden brown on the second side, about 2 minutes more. Transfer the chicken to a plate (it may not be cooked through).

Step 3

Heat the remaining 1 1/2 teaspoons olive oil in the skillet and repeat browning the remaining chicken. Transfer to the plate.

Step 4

Add 1/4 cup water and the remaining 1/4 teaspoon kosher salt to the skillet and scrape up any browned bits from the bottom. Add 1 bunch trimmed asparagus in an even layer. Cover and cook until almost crisp-tender, stirring halfway through, 1 to 3 minutes total.

Step 5

Add 3 tablespoons unsalted butter. When melted, return the chicken and any accumulated juices on the plate to the skillet. Stir in 4 minced garlic cloves and 1/4 teaspoon red pepper flakes if using. Cook, stirring occasionally, until the chicken is cooked through and the asparagus is bright green and crisp-tender, 2 to 3 minutes more. Garish with chopped fresh parsley leaves if desired.