In a large zip top bag or bowl, toss the chicken thighs, vinegar, mustard, brown sugar, salt, garlic, onion, chili, and smoked paprika until everything is well combined and the thighs are coated. Marinate for 45-90 minutes in the refrigerator.
5-6 chicken boneless skinless chicken thighs, pat dry, 2 Tablespoons apple cider vinegar, 1 Tablespoon Dijon mustard, 1/4 cup brown sugar, 1 1/2 teaspoons Morton kosher salt, 1 teaspoon EACH granulated garlic, onion powder, chili powder, & smoked paprika