Place 200gm cooking salt onto a large baking tray and place the oysters in rows of 4 on top of the salt.
For the mornay sauce place the butter into a small saucepan and melt over medium heat until melted. Add the flour and cook it out over medium heat for 1 minute. Once the flour is cooked out add the milk and return to the heat and whisk continually until the sauce is thick and smooth. Remove the sauce form the heat and whisk in the Dijon mustard, pour the sauce into a mixing bowl and set aside.
Place the spinach onto a perforated tray and into a pre-heated oven steam setting 100 °C for 4 minutes. Once steamed remove the spinach and place it into a colander over a bowl. Squeeze as much liquid out of the spinach as possible. Place the spinach onto the chopping board and roughly chop it and set aside.
Next finely slice the pancetta, dice the shallot and pick the thyme. Heat a medium size frypan over medium heat and add the sliced pancetta to the frypan. Fry for 2 minutes until the fat begins to render. Next add the diced shallot and thyme and cook for a further 1-2 minutes.
Remove the pancetta mix from the heat and place it in a small mixing bowl. Add tomato sauce, worstershire sauce and Tabasco to taste and mix well.
Place generous spoons of the pancetta mix onto 4 oysters and do the same with the Dijon mornay on another 4 oysters. Add chopped spinach to another 4 oysters and top the spinach with grated gruyere.
Place the tray into a pre-heated oven combi setting 210 °C for 12-15 minutes.
While the oysters are cooking make a salt mix for the oysters to sit on by mixing the remaining salt with a little dash of cold water.
Place the salt mix onto a large serving platter and when the oysters are done remove them from the oven and transfer to the “salted platter and serve.