Wash and disinfect the vegetables. Dice the cucumber (I remove the seeds). Finely chop the parsley and cut the leek into thin strips.

Dice the fresh tuna. Squeeze the limes and marinate the tuna with the juice, salt, and pepper. After 10 minutes, add the orange juice, soy sauce, parsley, cucumber, and adjust the seasoning to taste.

In an air fryer, add the leek strips with a drizzle of oil and cook for 8 minutes at 350°F (180°C) until crispy. To assemble the tostadas, spread mayonnaise on each tostada shell, top with the tuna mixture, and garnish with black sesame seeds and the crispy leek.