Whisk ¼ cup oil, garlic, lemon zest, coriander, cumin, 1 ½ tsp salt, ½ tsp pepper, nutmeg, and cinnamon together in medium bowl. Transfer 2 tbsp marinade to small bowl and set aside. Combine remaining marinade and pork in 1 gallon zipper lock bag and toss to coat. Press out as much air as possible and seal bag. Refrigerate for at least 1 hour or up to 2 hours, flipping bag every 30 minutes.

Whisk honey into reserved marinade and microwave until fragrant, 15 to 30 seconds. Remove pork from bag and pat dry with paper towels. Thread pork tightly onto four 12 inch metal skewers. Thread onion rounds from side to side onto two 12 inch metal skewers, brush with 1 tbsp oil, and season with salt and pepper.

Turn all burners to high, cover, and heat grill until hot, about 15 minutes. Turn all burners to medium-high.

Clean and oil cooking grate. Place pork and onion skewers on grill and cook covered, turning skewers every 2 minutes and basting pork with honey mixture, until pork is browned and registers 140 degrees and onions are slightly charred and tender, 10 to 15 minutes. Transfer pork and onions to cutting board as they finish grilling and tent loosely with aluminum foil. Let pork rest while preparing relish.

Coarsely chop onions and combine with remaining 1 tbsp oil, olives, capers, vinegar, and parsley. Season with salt and pepper to taste. Using tongs, slide pork off skewers onto serving platter. Serve pork with relish.