Fire up your grill for medium-high direct cooking.
While waiting for the grill to get hot, combine the butter, garlic, cheese, parsley and salt and pepper in a small bow.
Using a spatula, spread half of the mixture on one side of the bread slices and transfer (buttered side UP) to a baking sheet. Don't do the other side just yet (see my write-up as to why I do it this way).
Carry the baking sheet and remaining butter mixture to the grill. Get ready to move fast. Have your grill tongues ready.
Working one piece at a time, pick up the bread and slather the unbuttered side with the remaining butter. Transfer to the grill.
Keep buttering the bread and placing onto the grill, but keep an eye on the pieces you've already put on the grates. The butter will drip down and flare up and you might have to move the pieces away from any flames.
You'll want to flip the pieces after 1-3 minutes, once you have some grill marks and a little char on the bread. Same story goes for when you flip them: the butter might drip down and cause flare ups so be ready to move them if needed.
Grill another 1-3 minutes. Once nicely golden brown and slightly charred remove to the baking sheet and serve.