In a small sauté pan over medium heat add 1 tbsp (15 ml) of oil. Add onions, season with salt and 1/4 tsp (1 ml) of pepper and cook for 3 to 4 minutes or until onions are soft and translucent.
Add apples and cider vinegar and continue to cook for another 3 to 4 minutes or until apples are soft. Remove pan from the heat and let cool slightly.
Meanwhile, lay the lamb flat on a cutting board and make a horizontal cut through the centre of the lamb and open the two sides like a book. Place the cooled apple mixture inside and close the two sides of the lamb. Using butcher twine, gently tie the lamb to enclose the filling and ensure even cooking.
In a small bowl, add rosemary, thyme, sea salt and remaining pepper and oil; stir to combine. Gently rub the rosemary mixture over the surface of the lamb. In a lightly oiled roasting pan, add the lamb and place in the oven.
Let roast for 40 to 50 minutes, basting occasionally with pan juices. Once lamb is cooked to medium-rare 160°F (70°C) (or desired doneness) remove pan from the oven and let the lamb rest for 8 to 10 minutes before slicing.
Per serving: 600 calories, 41 g protein, 46 g fat (18 g saturated fats), 4 g carbohydrates, 1 g fibre, 155 mg cholesterol, 540 mg sodium, %RDI: Iron 20%