For the mayonnaise:
Put all the ingredients except the oil in a bowl and mix well. Now add the oil while whisking and straining until it thickens. Season to taste with salt and pepper.
Rub the bread slices with vegetable oil and grill them on the Shichirin grill over hot Binchotan.
Peel the shallots and cut them lengthways into quarters. Roast them lightly on the grill until they start to turn slightly black and are al dente, and cut them into strips.
Pull the oyster mushrooms into coarse pieces, sprinkle with vegetable oil and a little chopped garlic. Now lightly fry them on the grill over the hot Binchotan until they begin to colour and are cooked. Put them in a bowl and finish with olive oil, fleur de sel, chopped parsley and lemon juice for the garnish.
Serve the mushrooms on the toast with a few sprinkles of mayonnaise and the shallot.