In a small bowl, put vinegar, oil, oregano, garlic, salt and pepper and mix until combined.
Put chicken in a Ziploc bag. Pour vinegar mixture in bag with chicken, seal bag and spread marinade over chicken. Refrigerate for 30 minutes to overnight.
Preheat oven to 400 degrees. Spray small baking dish with cooking spray.
Put chicken in prepared baking dish and pour marinade over chicken. Cover and bake for 35 to 40 minutes, or until chicken is cooked thoroughly. Let sit for 5 minutes and then serve.