Toast the bread slices on both sides under a preheated medium grill or in a preheated ridged griddle pan or over a barbecue. Rub 1 side of each toasted slice with the bruised garlic, then drizzle with the oil and sprinkle with the parsley.
Pick over the porcini and brush off any grit. Remove the stalks and thinly slice. Slice the caps as thinly as possible.
Cut the toasted slices in half. Scatter over the sliced porcini stalks, drizzle with a little lemon juice and season with salt and pepper. Cover with the sliced porcini caps. Drizzle with more lemon juice and a little truffle oil, season again with pepper and garnish with a little chopped parsley. Serve immediately.