This is a favorite whether for breakfast, lunch or merienda. Its easy to make and you can have some variety with the cheese, tuna and breads. I haven't tried multiple cheeses but these are common in other tuna melt sandwiches restaurants or delis offer. You can get good bread from French Baker, Lartizan or off the shelf in major supermarkets. Canned tuna is available in most supermarkets and groceries. I can't imagine the effort to make tuna flakes from raw tuna from the wet market. If I had to buy my tuna melt sandwich, I prefer the one by Wild Flour. To-go, that would probably be by Starbucks. But that assumes I didn't have time to make one for myself.
-