Greek Lamb with Tzatziki Sauce (2 hour marinade)

2-1/2 to 3 pounds boneless leg of lamb
8 cloves garlic, divided
1/4 cup Dijon mustard
2 tablespoons minced fresh rosemary leaves
2 teaspoons salt
2 teaspoons black pepper
1/4 cup plus 2 teaspoons olive oil, divided
1 small seedless cucumber, peeled and grated, remove excess moisture
1 tablespoon chopped fresh mint
1 teaspoon lemon juice
2 cups plain nonfat or regular Greek yogurt

Directions

1. Untie and roll lamb to lie flat. Trim fat
2. For marinade: Mince four garlic cloves in small bowl. Add mustard, rosemary, salt and pepper and whisk in 1/4 cup oil. Spread evenly over lamb and place in large resealable bag in refrigerator for at least two hours or overnight, turning several times
3. For sauce: Mince four garlic cloves and mash to a paste. Add cucumber, mint, two tablespoons oil and lemon juice. Add yogurt and mix well then refrigerate.
4. Prepare grill for direct cooking. Grill lamb over medium-high heat for 35-40 minutes or until 140 degrees F. Let rest for five minutes.
5. Slice lamb and serve with sauce.