In a large skillet, cook lamb over medium-high heat until almost completely browned, approximately 4–5 minutes, stirring often. Stir in onions, garlic, oregano, paprika, fennel, and pepper; continue to cook 4–5 minutes, until the onions are almost golden. Adjust seasoning with salt. Remove from heat; keep warm until ready to serve. For each serving, place 1–1/2 cups warmed pita chips in a wide soup plate; top with 1 cup lamb-onion mixture. Sprinkle with 1/4 cup tomatoes, two tablespoons scallions, two tablespoons feta, and two tablespoons olives. Top with two tablespoons yogurt and garnish with a sprig of mint. Serve hot.