In a large bowl whisk the marinade ingredients, including 2 tablespoons salt and 2 teaspoons pepper. Add the turkey breast to the bowl, turn to coat evenly with the marinade, and cover with plastic wrap. Alternatively, place the turkey breast in a jumbo resealable plastic bag and pour in the marinade. Press the air out of the bag and seal tightly. Turn the bag to distribute the marinade and place in a large bowl. Refrigerate the turkey for 12 hours, turning occasionally.
Remove the turkey from the bowl or bag and pat dry with paper towels. Discard the marinade. Brush the turkey with oil, and allow to stand at room temperature for 1 hour before grilling.
Place a large disposable foil pan underneath the cooking grate to catch the drippings. Prepare the grill for indirect cooking over medium heat (350° to 450°F).
Brush the cooking grates clean. Grill the turkey breast, skin side up, positioned over the foil pan, over indirect medium heat, with the lid closed, until the skin is golden and the internal temperature reaches 160° to 165°F in the thickest part of the breast (not touching the bone), 1 to 1¼ hours. Meanwhile, prepare the potatoes and brussels sprouts.
In a medium bowl whisk 2 tablespoons oil, the granulated garlic, 1 teaspoon salt, and ¼ teaspoon pepper. Add the potatoes and turn to coat evenly. In another medium bowl whisk 2 tablespoons oil, ½ teaspoon salt, and ¼ teaspoon pepper. Add the brussels sprouts and turn to coat evenly.
About 10 minutes before the turkey is done, preheat a perforated grill pan over direct heat.
Remove the turkey from the grill and let rest for 15 to 20 minutes (the internal temperature will rise 5 to 10 degrees during this time). While the turkey rests, grill the potatoes on the grill pan over direct medium heat, with the lid closed, until tender and browned, about 15 minutes, turning often. Transfer the potatoes from the grill pan to a serving bowl and cover to keep warm. Grill the brussels sprouts on the grill pan over direct medium heat, with the lid closed, until crisp-tender, about 8 minutes, turning occasionally. Transfer the Brussels sprouts to a serving bowl. Cut the turkey into slices and serve warm with potatoes and brussels sprouts.