Preheat oven to 400ºF. Lightly spray a baking dish. Season turkey breast with salt and pepper.
In a large skillet, melt 1 Tbsp butter over mid-high heat. Brown turkey breast for 2 minutes per side.
Remove to prepared pan. And arrange onion and orange slices around pan.
In a small bowl mix sauce ingredients. Pour over turkey. Bake for 35-40 minutes or until an instant-read thermometer reads 170ºF (75ºC). Let stand before slicing.
NOTE: Sauce ingredients can be mixed, added to a zipper bag with turkey breast and marinated in refrigerator up to 24 hours. Marinade should be added to the skillet after turkey is removed (step #2) and brought to the boil for 2 minutes before pouring over turkey in roasting pan (step 4).