Cut 3 slits on the branzino using a sharp knife, you don't need to cut all the way through.
In a medium sized bowl mix the olive oil with shallots, mince garlic, parsley, dill, Aleppo pepper, salt and lemon juice. Spoon half this mixture inside the branzinos. Place the lemon slices in the cavity of the branzinos and seal it using a couple of toothpicks. Place the branzinos on a baking sheet and spoon the rest of the lemon herb mixture on top.
While the fish is being marinated, prepare the grill to high. You can use charcoal or gas grill. Rub half of a potato on the grates to avoid the fish sticking.
Place the branzinos on the grates and grill for about 8 minutes on each side. Flip only once. It's okay if the skin sticks to the grates. Grill the branzino until the skin is brown and crispy and the fish is cooked completely.
Make the tomato herb relish. In a medium sized bowl mix the tomatoes with the jalapeno, cilantro, parsley, red onion, lemon juice, olive oil, salt, pepper and sumac.
Place the grilled branzino on the platter and top with the tomato herb relish. Serve immediately.