Cut the zucchini into 4 long slices 1 centimetre thick (the rest is not used) and then halve them in width so that 8 slices are made in total.
Divide the salmon into 4 flat, thin slices. Distribute the mini gratins on a baking tray and place them in a preheated oven at 200 degrees for about 8 minutes.
Season the salmon slices with salt and pepper. Coat the courgette on both sides with pesto and dust them with a mixture of breadcrumbs and Parmesan cheese.
Place the salmon slices and the courgette next to the gratins on the baking tray and put it back in the hot oven for about 8 minutes. Stack 3 mini gratins on 1 slice of courgette on each preheated plate, top with another a slice of courgette and finish with a slice of salmon.
Garnish the gratin sandwiches with lemon, herbs and some drops of oil.