Make lamb: In a small bowl, combine 3 tbsp oil, the zest, juice and garlic. In another bowl, combine 2 tsp salt, the mustard powder, pepper, celery seed, nutmeg and allspice.

Heat oven to 375 degrees F. Place one rack in center and one rack on lowest level. Rinse lamb and pat dry. Place, fat side up, in a large roasting pan. Using a sharp paring knife, make 15 to 20 small slits around lamb. Generously rub lemon mixture over entire surface of lamb. Follow with dry spice mixture, pushing into slits.

Roast lamb in center of oven until an instant-read thermometer inserted into thickest part (without touching bone) registers 130 degrees F for medium rare, about 1 hr 45 min.

Meanwhile, on a rimmed baking sheet, toss together fennel, lemons, remaining 2 tbsp oil and 1/2 tsp salt. After 1 hr of roasting lamb, place fennel and lemons on sheet on lower rack. Roast, turning once, until fennel is golden and tender, about 40 min.

Loosely tent lamb with foil; let stand 15 min before carving. Transfer to a platter; arrange fennel and lemons around lamb.

Make chutney: Meanwhile, in a medium saucepan, melt butter over medium-high heat. Add onion and cook, stirring, until softened, about 4 min. Stir in apple, sugar, raisins, vinegar, salt, nutmeg and 1/3 cup water. Bring to a boil, reduce heat to medium and cook, stirring occasionally, until apple is tender and mixture has thickened slightly, about 8 min.

Remove from heat and stir in mint. Serve with lamb. Makes 6-8 servings and about 2 cups chutney.