Bring to Room Temperature: Let the lamb sit out for about 1 hour so it cooks evenly.
3 pounds boneless leg of lamb trimmed and tied
Preheat Oven: Heat oven to 450°F.
Make Herb Paste: Blend garlic, parsley, rosemary, mint, oregano, lemon zest, salt, pepper and olive oil in a food processor until smooth.
5 garlic cloves roughly chopped, 2 tablespoons fresh parsley chopped, 1 tablespoon fresh rosemary chopped, 1 tablespoon fresh mint chopped, 1 teaspoon dried oregano, 1 tablespoon lemon zest, 2 teaspoons kosher salt, 1/2 teaspoon black pepper, 1/4 cup extra virgin olive oil
Coat the Lamb: Rub the paste all over the lamb and place it in a roasting pan.
Start Roasting: Roast uncovered for 15 minutes to develop a browned crust.
Prep Vegetables: While the lamb starts cooking cut potatoes and slice fennel into even pieces.
2 pounds baby potatoes halved or quartered, 1 fennel bulb trimmed cored and thinly sliced
Add Vegetables and Lower Heat: Reduce oven to 400°F. Scatter vegetables around the lamb and toss them with the pan drippings. Season lightly with additional salt and pepper.
Additional salt to taste, Additional black pepper to taste
Finish Cooking: Roast 40–45 minutes more or until the thickest part reaches 130°F for medium rare.
Rest the Lamb: Transfer lamb to a board, tent with foil, and rest 15 minutes.
Crisp the Vegetables: If needed continue roasting vegetables a few minutes longer until golden and tender.
Slice and Serve: Remove twine, slice thinly, and serve with the roasted vegetables and pan juices.