Preheat your oven to 275°F (135°C).
Place the leg of lamb on a clean work surface. Use a sharp knife to make small incisions all over the lamb, about 1 inch apart.
In a small bowl, combine the minced garlic, coarse salt, and Italian herbs blend. Rub the garlic and herb mixture all over the lamb, making sure to get it into the incisions you made. This will infuse the lamb with flavor as it cooks.
Place lamb it on a rack and set inside a roasting pan.
Insert the halved garlic cloves into some of the incisions you made earlier.
Roast the lamb in the preheated oven for about 1 1/2 to 2 hours, or until it reaches your desired level of doneness. Use a meat thermometer to check the internal temperature:
130°F (54°C) for medium-rare
140°F (60°C) for medium
150°F (66°C) for medium-well
Heat the avocado or olive oil in a large ovenproof skillet or roasting pan over medium-high heat. Once the oil is hot, add the lamb to the skillet. Sear the lamb on all sides until it develops a golden-brown crust, about 2-3 minutes per side.
Remove lamb from the oven and let it rest for 15-20 minutes. This allows the juices to redistribute and keeps the meat moist. Carve the lamb into slices and serve.
If desired, you can make a simple gravy using the pan drippings. Place the roasting pan with the drippings on the stovetop over medium heat. Add a little flour and whisk until it thickens into a gravy.
Serve the reverse-seared leg of lamb slices with your choice of side dishes, such as roasted vegetables, mashed potatoes, or a fresh salad.