In a large bowl toss together 1 tablespoon of olive oil and next 7 ingredients (fennel through vinegar).
Cut 5 slits into pork tenderloin and push a clove of garlic into each. Rub with remaining tablespoon of oil and place in roasting pan then season with salt and pepper. Pour the fennel mixture into roasting pan on all sides.
Place the tenderloin in the oven and roast for 45 minutes to an hour or until tenderloin is cooked through. Serve with a scoop of fennel and onions.