Toast bread lightly and butter to taste. Wash the tomatoes and zucchino, cut into thin slices and spread on the toast. Salt and pepper.
Peel the onion and cut into thin slices, spread on the toast. Also cut the olives into thin slices and spread them on the toast. Spread a few thyme leaves on the toast slices, then cover everything with Bel Paese slices.
Bake at 200 degrees (fan oven) for about 4 minutes until the cheese melts. Then, depending on the taste and the desired browning of the cheese, place it under the grill for about 1 minute.