Preheat oven to 400 degrees F. Place onion slices in the bottom of a baking dish that will fit your pork loin.
In a small bowl, mix together the salt, pepper, thyme, garlic powder and paprika. Sprinkle liberally over the pork loin and gently press. Starting at one end, wrap the a slice of bacon around the pork loin. Slightly overlap the second slice and continue wrapping with bacon until completely wrapped. You can use toothpicks to secure the bacon if you're having trouble with it unraveling. Place the pork on top of the onion.
Insert a digital meat thermometer and set to 140 degrees F, if using. Bake pork loin for 35 to 45 minutes, until cooked through.
If bacon isn't crispy enough, turn on the broiler and let cook another minute or two until the bacon crisps. Keep a close eye on it so it doesn't burn.
Remove from oven and let rest 10 minutes before slicing.