Lemon Pepper Chicken Salad

Name: Lemon Pepper Chicken Salad
Ingredients: 1½ lb. skinless, boneless chicken thighs (about 6 medium), patted dry; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, plus more; 1 Tbsp. lemon pepper, plus more for serving; Extra-virgin olive oil (for drizzling); 1 large garlic clove, finely grated; ½ cup sour cream; ¼ cup mayonnaise; 4 Tbsp. fresh lemon juice, divided; 2 heads of Little Gem or romaine lettuce, leaves separated; 4 celery stalks, thinly sliced; ½ small red onion, thinly sliced; Freshly ground pepper