Cut the tuna fillets into thin slices, approximately ½ centimeter thick. In a medium-sized bowl, combine honey with soy sauce and lemon juice. Place tuna slices inside the mix and leave them marinating for 3-4 hours in the refrigerator.
In a small bowl, mix mayonnaise, chives, a tablespoon of chipotle paste and salt and pepper to taste. Set aside.
Cut the white portion of the leeks into thin strips and heat in a frying pan with the olive oil. Fry leeks in small quantities until browned and crispy. Place on paper towels to absorb the excess oil.
Spread the mayonnaise mix on each mini tostada and top with the marinated tuna slices. Cut avocados in thin slices and distribute them evenly onto tostadas. Garnish with a bit of fried leeks and serve.
For the chipotle paste:
Clean the chipotle peppers and remove all the seeds. Put them in a blender with the water or chicken stock. Blend until perfectly mixed. It can keep for weeks in the refrigerator and is a good base for preparing chipotle sauce or for flavoring other dishes.
If you are unable to find packaged mini tostadas, use 8 tortillas and cut each one using a round cookie cutter, focusing on the center of the tortilla to obtain a mini tortilla. Preheat oven to 350°F and place all the mini tortillas on a baking sheet in one single layer. Lightly spray each mini tortilla with olive oil. Bake for 7 minutes. Turn the baking sheet and bake for another 7 minutes or until they look crunchy. Let cool before serving.