In a large container, mix together buttermilk, onions, 1½ tsp salt, ¾ tsp pepper, dry mustard, and vinegar. Add Chicken. Refrigerate for at least 30 mins.

Preheat oven to 425. Combine bread crumbs, paprika, remaining ½ teaspoon salt and ¼ teaspoon pepper, and thyme in a shallow bowl. Take the chicken out of the marinade, dredge the pieces in the bread crumb mixture. Coat all sides with Cooking Spray.

Place the chicken on a baking rack over a baking sheet. Bake for at least 30-35 minutes or internal temp is 180 degrees.