“If your grill is not ripping hot, the greens will wilt. In addition, you risk the greens falling through the grill grates,” says Brian Jupiter, the executive chef of Frontier Chicago and Ina Mae Tavern, both in Chicago. He says another way to char greens is to “use a cast iron pan on the highest heat on your stovetop. Or, if you’re set on using the grill, crank the grill up to its highest heat for 20 minutes, then place the cast iron pan filled with your greens on the grill grates to begin cooking.”
Article source: https://www.huffingtonpost.co.uk/entry/ffood-you-should-never-cook-on-a-bbq-expert-advice_uk_62acb347e4b06594c1d61d4b