If we use not only the fish filling, you can add the tomato to the ingredients.

French bread (baguette) cut into the projected portion. Each sandwich in half lengthwise 1/3 from the top, i.e. so that the sandwich came the lid, the lid put aside and work with the bottom part of the sandwich. Making hands the crumb inside.

Smear the bottom part with mayonnaise mixed with chopped garlic, put lettuce, onion roughly chopped, tuna, again grease mayonnaise, put a slice of cheese, cover with a lid and put either in the microwave for a few minutes or in the oven for 5-10 minutes. Bon appetit!