Prepare the Marinade: In a medium bowl, whisk together the white vinegar, spicy brown mustard, minced garlic, lemon juice, light brown sugar, salt, olive oil, and freshly ground black pepper.

Marinate the Chicken: Place the chicken breasts in a large resealable plastic bag or shallow dish. Pour the marinade over the chicken, making sure all pieces are well coated. Close the bag tightly or cover the dish with a lid, then place it in the refrigerator for at least 30 minutes, though letting it chill for 2-4 hours will enhance the flavor even more.

Cook the Chicken: Preheat your grill, oven, or skillet to medium heat. Remove the chicken from the marinade, shaking off any excess, and cook for 6-8 minutes per side, or until the internal temperature reaches 165°F (75°C) and the chicken is cooked through. Discard any remaining marinade.

Serve: Let the chicken rest for 5 minutes before slicing and serving. Enjoy alongside your favorite sides like roasted vegetables, rice, or a fresh salad.