Make the za’atar: (Skip to the next step if you’re using store-bought za’atar.) Mixing well, combine all za’atar ingredients at left. Set aside.
Prepare the dish: Using a very sharp knife, preferably a slicing knife, make long slices perpendicular to the grain of the muscles in the fish. The lines that you see are the direction of the grain—you are slicing across them, not with them. Make long, careful strokes using the whole length of the blade, by pulling back with your elbow and letting the knife do the work; do not push with the knife or “chop” the fish. Slices should be as thin as you can get, about 2 millimeters for a firm-fleshed fish. Depending on the size of the loin, you are looking for 6–9 slices, or 3 ounces.
Place 1 tbsp za’atar on the plate next to the sliced fish, and pour a glug of smoked olive oil over the fish and the za’atar. Finish by crushing the Maldon salt between your fingers directly over the fish. Top with cilantro. Serve with warm bread.