Brush the tenderloins with the cinnamon mixture and season to taste with salt and pepper.
Melt some cooking fat and brown the tenderloins in an ovenproof skillet placed over a medium-high heat. Transfer the browned tenderloins to a plate and set aside.
In the same skillet, brown the onion and garlic.
Add the remaining ingredients and bring to a boil, scraping the bottom of the skillet to get all the browned bits into the sauce.
Return the tenderloins to the skillet.
Place in the oven and roast for 15 to 20 minutes, or to desired doneness.