In a bowl, combine the pepper jack cheese, olives, butter, cream cheese, and garlic powder with a hand-held mixer until smooth. Slather the cheese mixture over the cut halves of bread and sandwich the halves together.
Wrap the loaf in aluminum foil and put on the grill, or if broiling under the broiler. Grill or broil, 4 inches from the heat, turning once, until the edges of the bread are crisp and golden and the cheese mixture is melted, about 10 to 15 minutes total. Transfer the bread to a cutting board, slice and serve hot.