In a small bowl, whisk together 1/4 cup lemongrass powder, 1/4 cup olive oil, 1/4 cup soy sauce, 1/4 cup lime juice, 2 tablespoons Worcestershire sauce, 1 teaspoon garlic salt, and 1 teaspoon lemon pepper until smooth.
Place the 4 chicken thighs in a large zip-top bag or shallow dish and pour the marinade over them.
Seal the bag, removing as much air as possible, and massage the marinade so the chicken is evenly coated.
Refrigerate and marinate the chicken for 30–60 minutes (or up to 24 hours if desired).
Preheat the air fryer to 350°F.
Arrange the chicken in the air fryer basket skin-side down in a single layer without overcrowding.
Cook for 10 minutes, then flip the thighs and cook an additional 7–8 minutes, or until an instant-read thermometer inserted into the thickest part registers 165°F.
Remove the chicken and let it rest for 5 minutes before serving.
Garnish with minced fresh scallions, if using, and serve.