Combine garlic, prunes, olives, capers, olive oil, red wine vinegar, bay leaves and oregano together in a 9x9" glass baking dish or similarly sized casserole dish. Add chicken thighs and toss to coat the chicken. Cover and refrigerate the dish overnight to marinate.
Heat oven to 350°F. Sprinkle the brown sugar evenly over the chicken and pour the water over the top. Bake until the center of the thighs measure 165°F on an instant-read thermometer, 45-60 minutes. Sprinkle with parsley, if desired.
Notes
Pitted green olives that are plain, or stuffed with pimento or garlic can be used.