Prepare a charcoal or gas grill to high heat. Place a large cast iron skillet on the grill grate, directly over the heat. Warm olive oil in the skillet, then add the garlic and red chile flakes. Cook, stirring frequently, until the garlic is golden (1 - 2 minutes). Add the mussels, white wine, a couple pinches of salt and several turns of black pepper, stirring to combine. Loosely cover the skillet with a sheet of foil*, cover the grill, and cook until all the mussels have opened (about 5 - 7 minutes). Discard any mussels that haven’t opened.
You can serve the mussels directly from the skillet or pour into a serving bowl with juices. To finish, sprinkle parsley, mint and lemon zest over top. Serve grilled bread on the size, and have a bowl ready to collect empty shells.
Notes
* I simply draped a piece of foil over the skillet. The foil will help the mussels steam, but you want to leave some breathing room so the smoke can get in and add flavor.