Finely chop or press the garlic. Finely dice the onion.
Squeeze the lemons, add the juice to the garlic and onion cubes. Add oil and vinegar and stir well with a whisk. (Oil should not form greasy eyes) Add water. Stir in the ketchup and mustard.
Now mix the sauce with the herbs and spices.
Rinse and pat dry the meat, then score lightly.
Brush the first slice of meat with the marinade on both sides and place in a bowl. Only coat the following slices on the upper side, as the lower, uncoated side is placed on an already marinated disc.
Pile the meat in the bowl. At the end pour the rest of the marinade over the meat and cover it in the fridge for 6-12 hours.