Xinjiang grilled lamb chops

Ingredients

• 1 rack of lamb ribs (about 1.5 kg)
• 2 tbsp cumin powder
• 1 tbsp chili powder
• 1 tsp salt
• 1 tsp black pepper
• 3 cloves garlic (minced)
• 2 tbsp vegetable oil
• 1 onion (quartered)