1. Saute onion and garlic in vegetable oil. Add cumin and cayenne, and simmer 20 minutes.
2. Transfer onion-garlic mixture to a bowl, scraping the pan with a spatula to get all the spiced oil. Add the rest of the ingredients and mix well.
3. Brush over meat as it sizzles on the grill, or pour over meat in a roasting pan and bake, or transfer sauce and shredded cooked meat to a saucepan and simmer until heated through, 15 to 20 minutes.