Steps
1. Preheat the grill to medium-high heat.
2. Clean and gut the mackerel, removing the scales and any innards.
3. Rinse the mackerel under cold water and pat dry with paper towels.
4. Slice the lemon and garlic cloves.
5. Stuff the mackerel cavity with lemon slices, garlic, thyme, and rosemary sprigs.
6. Drizzle the olive oil over the mackerel and season with salt and pepper.
7. Place the mackerel on the grill and cook for about 4-5 minutes on each side, or until the fish is cooked through and flakes easily with a fork.
8. Remove the mackerel from the grill and serve hot.
9. Garnish with additional lemon slices and fresh herbs, if desired.