In a large bowl using your hands, gently combine the meat loaf ingredients.
Divide the meat loaf mixture in half and form into two loaves, each about 4 inches wide and 6 to 7 inches long. Place the loaves on a sheet pan.
Prepare the grill for indirect cooking over medium-low heat (about 350°F).
In a small bowl mix the sauce ingredients. Set aside half of the sauce to serve with the meat loaf. Top each meat loaf with 3 tablespoons of the remaining sauce and coat thoroughly.
Brush the cooking grates clean. Using a metal spatula, gently pick up each loaf from the sheet pan and place directly on the cooking grate. Grill the meat loaves over indirect medium-low heat, with the lid closed, until a thermometer inserted horizontally through the top of each loaf registers 155°F, 50 minutes to 1 hour. Remove the loaves from the grill and let rest 10 to 15 minutes. Once removed from the grill, the loaves will continue to cook, allowing them to reach the recommended 160°F for ground beef and pork. Cut the loaves into slices and serve with the reserved sauce.
To make meat loaf sandwiches, cut the meat loaf into ½-inch-thick slices and slather both sides with some of the reserved sauce. Grill over direct low heat (250° to 350°F), with the lid closed as much as possible, for 4 to 6 minutes, turning once. Serve on sourdough bread. Also great with melted provolone cheese.