Not always garlic but we make buttered/oiled/herbed/etc. toasted breads all the time on the grill. I usually do it while whatever meat we're having is resting.
If it was a long cook (coals almost spent), I do it directly over the coals, peeking often and turning/removing when it's the color I'm looking for.
If it was a short cook (coals still very hot), I do the same thing but at the edge of the coals...not really direct but not really indirect either.
The key is that you have to stay right there, watch it closely and not leave the grill. It goes from perfect to burned in an instant.