Slice the boneless elk into 1-inch pieces and set aside.
In a small bowl, whisk together ½ cup olive oil, lemon juice, lemon zest, vinegar, minced garlic, Greek oregano and salt. Add the elk to a large bowl or freezer bag and coat the meat with the marinade. Marinate the meat for 1-2 hours in the refrigerator.
In a bowl, combine all yogurt sauce ingredients and refrigerate until ready.
Thread the elk onto skewers and discard any remaining marinade. Thread the vegetables separately onto skewers, drizzle with remaining olive oil and season with salt. (If using wooden skewers, soak in water for 10 minutes prior to threading.)
Preheat grill to medium-high heat. Add the skewered meat and vegetables and grill 8-10 minutes, rotating throughout to ensure even cooking.
Serve the grilled elk with vegetables, naan bread and yogurt sauce.