Preheat the oven to 475°F.

Place lamb in a roasting pan fitted with a rack.

Put garlic, fennel seeds, salt and pepper in a food processor.

Pulse until coarsely ground, stopping to scrape down the sides of the bowl several times.

Transfer mixture to a small bowl and stir in a tablespoon of the oil.

Rub mixture over lamb.

Roast lamb 10 minutes.

Lower oven temperature to 300°F and continue roasting until lamb reaches desired doneness, about 1 1/2 hours for medium.

Transfer lamb to a cutting board and let rest 15 minutes.

While lamb rests, heat remaining 2 teaspoons oil in a large skillet over medium-high heat.

Add onions and fennel and cook 2 minutes.

Add wine, cover, and continue to cook until vegetables are very soft, about 10 minutes more.

Season to taste with salt and stir in mint leaves.

Carve lamb and serve slices with spring onion mixture.