• In a large bowl, whisk together the olive oil, vinegar, soy sauce, Worcestershire, lemon juice, brown sugar, rosemary, mustard, salt, pepper, and garlic powder until the mixture is fully emulsified and smooth.
• Set aside ½ cup of the marinade to use later for basting during cooking.
• Transfer the chicken into a large resealable plastic bag or shallow glass dish. Pour the remaining marinade over the chicken, sealing the bag or covering the dish tightly. Gently work the marinade into the chicken by massaging or turning pieces to coat evenly. For quicker absorption, lightly pierce the chicken with a fork prior to marinating.
• Refrigerate the marinated chicken for a minimum of 30 minutes or up to 24 hours. For optimal flavor infusion, aim for a marinating time of 4 to 6 hours.

To Grill:

• Preheat the grill to medium-high. Lightly oil the grates to prevent sticking. Remove the chicken from the marinade, allowing any excess to drip off. Grill each side for approximately 5 to 6 minutes or until the internal temperature reaches 165°F. Brush with the reserved marinade periodically during grilling.
• Once cooked, remove chicken from heat, loosely cover with foil, and allow to rest for at least 5 minutes prior to serving.
• Optional: For additional flavor, bring the reserved marinade to a boil in a saucepan, then reduce to a gentle simmer until thickened slightly. Serve this reduction as a finishing sauce over the chicken.

To Bake:

• Preheat oven to 400°F. Arrange the marinated chicken on a shallow baking tray. Roast for 18 to 22 minutes or until the internal temperature reads 165°F. For faster cooking, use a 450°F oven and bake for 15 to 18 minutes. Baste intermittently with reserved marinade. Rest 5 minutes before serving.

To Cook on Stovetop:

• Heat a lightly oiled skillet over medium-high heat. Place marinated chicken in the pan and cook for 8 to 10 minutes per side until the internal temperature hits 165°F. For grill marks, use a stovetop grill pan. Let rest for 5 minutes before serving.