In a small bowl, stir together oil and finely chopped rosemary.
In large pot, cover potatoes with salted cold water; bring to a boil and cook until tender, about 20 to 25 minutes. Drain. Place potatoes on cutting board; using bottom of a pot, press down to smash potatoes until they pop open. Let cool.
Heat barbecue to medium-high heat.
Brush potatoes with rosemary oil. Place on grill and cook, flipping a few times, until crisp, about 8 minutes. Sprinkle with salt and pepper.