Barbecue Chicken Sliders with Pickled Onions

Shredded chicken thighs cooked on the grill are dipped in Karolinska barbecue sauce-a mixture based on vinegar with mustard, a small amount of honey, seasonings and butter.
Preheat the grill to medium-high heat.Combine the chopped onion, 1 tablespoon vinegar, and 1 1/2 teaspoons honey in a small bowl; mix well. Cover and refrigerate the onion mixture for at least 30 minutes.Combine the remaining 2 tablespoons of vinegar, remaining 1 tablespoon of honey, 2 tablespoons of water, mustard, and 1/4 teaspoon of pepper in a small saucepan over medium-low heat. Bring to a boil (do not bring to a boil). Simmer for 5 minutes; drizzle with butter. Remove from heat; keep warm.Sprinkle the chicken with the remaining 1/2 teaspoon pepper and salt. Place on a grill rack greased with cooking spray; cook for 4 minutes on each side or until tender. Remove chicken from grill; cool slightly. Cut the chicken into small pieces. Add the chicken to the pan with the mustard mixture and gently stir to coat.Cut the rolls crosswise in half. Place the rolls, cut side down, on a wire rack; cook for 1 minute or until lightly browned. Place about 1/3 cup of the chicken mixture on the bottom half of each roll. Place about 1 teaspoon of chopped onion and the top half of the roll on each roll. Serve immediately.