Drain artichoke hearts, reserving marinade. Brush the bread shells with some of the reserved marinade (discard any remaining marinade). Sprinkle half of the fontina or mozzarella cheese over shells. In a large bowl toss together the artichoke hearts, Canadian-style bacon, tomatoes, feta cheese, green onions, and oregano; divide among shells. Sprinkle with remaining fontina or mozzarella cheese.
Transfer the bread shells to a pizza grill pan or a large piece of double-thickness heavy foil. On a grill that has a cover, place the pan or foil on the rack of the grill directly over medium heat. Cover and grill for 5 to 8 minutes or until cheese is melted and pizza is heated through. Makes 8 servings.