Combine the diced onion, lemon juice, bourbon, honey, soy sauce, gingerroot, minced garlic and 2 Tablespoons of olive oil in a large zippered bag. Add pork tenderloin and marinate in the refrigerator for 30 minutes.

Preheat oven to 425 degrees.

Once the pork has marinated, heat remaining 2 Tablespoons of olive oil over medium heat in a large skillet.

Remove the pork from the bag, reserving the marinade, and season the tenderloin with salt and pepper.

Sear pork in the skillet for a minute or two on each side, until lightly browned,

Transfer to a baking dish coated with cooking spray. Pour a ½ cup of marinade over the pork.

Cover with foil and roast for 20 to 35 minutes, until a meat thermometer registers 145 degrees to 160 degrees. Baste occasionally with pan juices while roasting.

Remove pork from oven and let rest for 5 minutes before slicing. Keep warm.

Prepare the gravy by combining flour and reserved marinade in a sauce pan, whisking to combine. Gradually add the water and bring to a boil over medium heat for about 3 minutes, whisking constantly, until thickened.