Preheat grill
In a small bowl, add garlic, rosemary and half of olive oil. Stir until well combined and set aside.
Place potatoes on a plate and microwave on high for around 4 minutes. Flip the potatoes over and microwave for another 4 minutes.
Brush potatoes with remaining olive oil and season with salt and pepper.
Once the grill is hot, lay sweet potato pieces down onto the grill. Cover the grill and cook until each side gets grill marks (around 3-6 minutes per side).
Spread the garlic and rosemary mixture over the top of potatoes. Cover and let cook another minute or until desired consistency.