In a deep casserole or roasting pan, combine 3 tablespoons olive oil, garlic, red-pepper flakes, orange zest, fennel, cardamom (if using), and ginger. Add lamb leg and turn to coat well. Cover and refrigerate at least 2 hours (or up to 12 hours).
In a medium sauté pan over medium-high heat, melt butter. Add rosemary and breadcrumbs. Stirring often, sauté 2 to 3 minutes, until breadcrumbs are lightly browned. Fold in parsley. Remove from heat and set aside.
Remove lamb from the refrigerator and bring to room temperature. Heat your broiler to medium high.
Remove lamb from marinade and place on a broiler pan or on a rimmed baking sheet that will fit under your broiler. Season both sides with salt and pepper. Place under the broiler, 3 to 4 inches from heat, for 5 minutes. Lower heat to 400°, lower oven rack to center, and cook another 5 minutes.
Remove lamb from oven. Carefully spread an even layer of olive tapenade all over lamb. Sprinkle feta cheese on top of tapenade. Then sprinkle a coat of seasoned breadcrumbs and press down gently.
Place lamb in oven and heat 8–10 minutes. Remove from oven and let rest 10 minutes before slicing.