Heat up the Outdooroven and make sure it burns for about 15 minutes to get an even temperature. Pack the sweet potatoes in aluminum foil, place the grill in the Outdooroven and place the sweet potatoes on the grill. They can lay in the fire but turn them regularly with tongs.
2. Meanwhile, clean the fennel, remove the hard parts, cut into parts and then into thin strips. Cut the parsley and mint fine without twigs, or crush into a mortar. Add olive oil, some pepper and salt to the finely chopped herbs and add lemon juice by squeezing the lemon. Mix well and add some grated zest of the lemon. Mix the fennel and dressing in a bowl and put in the refrigerator to keep it cool.
3. Check the sweet potatoes regularly, but let the fire slowly decrease to glowing woodblocks by not adding more logs.
4. Season the mackerel fillets with salt and pepper, and gently spread some olive oil on the skin. Put the sweet potatoes aside and place the mackerel on the grill (if the sweet potatoes are soft and done you can keep them warm in the oven). Grill the mackerel for about 4 to 6 minutes, or longer if necessary. Make sure to keep them away from the fire to prevent them from burning.
5. Put some fennel salad on a plate, take the mackerel fillets from the grill and place it on the salad. Take the sweet potatoes from the grill or from the oven as well, take them out of the foil carefully and cut them in half. Put them on the plate and garnish with the remaining salad dressing.